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MongoDB Sharding
This tutorial will show you how to use KubeDB to run a sharded MongoDB cluster.
Before You Begin
Before proceeding:
Read mongodb sharding concept to learn about MongoDB Sharding clustering.
You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube.
Now, install KubeDB cli on your workstation and KubeDB operator in your cluster following the steps here.
To keep things isolated, this tutorial uses a separate namespace called
demothroughout this tutorial. Run the following command to prepare your cluster for this tutorial:$ kubectl create ns demo namespace/demo created
Note: The yaml files used in this tutorial are stored in docs/examples/mongodb folder in GitHub repository kubedb/docs.
Deploy Sharded MongoDB Cluster
To deploy a MongoDB Sharding, user have to specify spec.replicaSet option in Mongodb CRD.
The following is an example of a Mongodb object which creates MongoDB Sharding of three members.
apiVersion: kubedb.com/v1alpha1
kind: MongoDB
metadata:
name: mongo-sh
namespace: demo
spec:
version: 3.6-v3
shardTopology:
configServer:
replicas: 3
storage:
resources:
requests:
storage: 1Gi
storageClassName: standard
mongos:
replicas: 2
strategy:
type: RollingUpdate
shard:
replicas: 3
shards: 3
storage:
resources:
requests:
storage: 1Gi
storageClassName: standard
$ kubectl create -f https://github.com/kubedb/docs/raw/v0.13.0-rc.0//docs/examples/mongodb/clustering/mongo-sharding.yaml
mongodb.kubedb.com/mongo-sh created
Here,
spec.shardTopologyrepresents the topology configuration for sharding.shardrepresents configuration for Shard component of mongodb.shardsrepresents number of shards for a mongodb deployment. Each shard is deployed as a replicaset.replicasrepresents number of replicas of each shard replicaset.prefixrepresents the prefix of each shard node.configSourceis an optional field to provide custom configuration file for shards (i.e mongod.cnf). If specified, this file will be used as configuration file otherwise a default configuration file will be used.podTemplateis an optional configuration for pods.storageto specify pvc spec for each node of sharding. You can specify any StorageClass available in your cluster with appropriate resource requests.
configServerrepresents configuration for ConfigServer component of mongodb.replicasrepresents number of replicas for configServer replicaset. Here, configServer is deployed as a replicaset of mongodb.prefixrepresents the prefix of configServer nodes.configSourceis an optional field to provide custom configuration file for configSource (i.e mongod.cnf). If specified, this file will be used as configuration file otherwise a default configuration file will be used.podTemplateis an optional configuration for pods.storageto specify pvc spec for each node of configServer. You can specify any StorageClass available in your cluster with appropriate resource requests.
mongosrepresents configuration for Mongos component of mongodb.Mongosinstances run as stateless components (deployment).replicasrepresents number of replicas ofMongosinstance. Here, Mongos is not deployed as replicaset.prefixrepresents the prefix of mongos nodes.configSourceis an optional field to provide custom configuration file for mongos (i.e mongod.cnf). If specified, this file will be used as configuration file otherwise a default configuration file will be used.podTemplateis an optional configuration for pods.strategyis the deployment strategy to use to replace existing pods with new ones. This is optional. If not provided, kubernetes will use default deploymentStrategy, ie.RollingUpdate. See more about Deployment Strategy.
spec.certificateSecret(optional) is a secret name that contains keyfile(a random string) againstkey.txtkey. Each mongod replica set instances in the topology uses the contents of the keyfile as the shared password for authenticating other members in the replicaset. Only mongod instances with the correct keyfile can join the replica set. User can provide theCertificateSecretby creating a secret with keykey.txt. See here to create the string forCertificateSecret. IfCertificateSecretis not given, KubeDB operator will generate aCertificateSecretitself.
KubeDB operator watches for MongoDB objects using Kubernetes api. When a MongoDB object is created, KubeDB operator will create a new StatefulSet and a ClusterIP Service with the matching MongoDB object name. KubeDB operator will also create governing services for StatefulSets with the name <mongodb-name>-<node-type>-gvr. No MongoDB specific RBAC permission is required in RBAC enabled clusters.
MongoDB mongo-sh state,
$ kubectl get mg -n demo
NAME VERSION STATUS AGE
mongo-sh 3.6-v3 Running 9m41s
Sharding and ConfigServer nodes are deployed as statefulset.
$ kubectl get statefulset -n demo
NAME READY AGE
mongo-sh-configsvr 3/3 11m
mongo-sh-shard0 3/3 10m
mongo-sh-shard1 3/3 8m59s
mongo-sh-shard2 3/3 7m45s
Mongos nodes are deployed as deployment.
$ kubectl get deployments -n demo
NAME READY UP-TO-DATE AVAILABLE AGE
mongo-sh-mongos 2/2 2 2 8m41s
All PVCs and PVs for MongoDB mongo-sh,
$ kubectl get pvc -n demo
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
datadir-mongo-sh-configsvr-0 Bound pvc-1db4185e-6a5f-11e9-a871-080027a851ba 1Gi RWO standard 16m
datadir-mongo-sh-configsvr-1 Bound pvc-330cc6ee-6a5f-11e9-a871-080027a851ba 1Gi RWO standard 16m
datadir-mongo-sh-configsvr-2 Bound pvc-3db2d3f5-6a5f-11e9-a871-080027a851ba 1Gi RWO standard 15m
datadir-mongo-sh-shard0-0 Bound pvc-49b7cc3b-6a5f-11e9-a871-080027a851ba 1Gi RWO standard 15m
datadir-mongo-sh-shard0-1 Bound pvc-5b781770-6a5f-11e9-a871-080027a851ba 1Gi RWO standard 15m
datadir-mongo-sh-shard0-2 Bound pvc-6ba3263e-6a5f-11e9-a871-080027a851ba 1Gi RWO standard 14m
datadir-mongo-sh-shard1-0 Bound pvc-75feb227-6a5f-11e9-a871-080027a851ba 1Gi RWO standard 14m
datadir-mongo-sh-shard1-1 Bound pvc-89bb7bb3-6a5f-11e9-a871-080027a851ba 1Gi RWO standard 13m
datadir-mongo-sh-shard1-2 Bound pvc-98c96ae4-6a5f-11e9-a871-080027a851ba 1Gi RWO standard 13m
datadir-mongo-sh-shard2-0 Bound pvc-a1eebcd2-6a5f-11e9-a871-080027a851ba 1Gi RWO standard 13m
datadir-mongo-sh-shard2-1 Bound pvc-b231fb18-6a5f-11e9-a871-080027a851ba 1Gi RWO standard 12m
datadir-mongo-sh-shard2-2 Bound pvc-c5bb265f-6a5f-11e9-a871-080027a851ba 1Gi RWO standard 12m
$ kubectl get pv -n demo
NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE
pvc-1db4185e-6a5f-11e9-a871-080027a851ba 1Gi RWO Delete Bound demo/datadir-mongo-sh-configsvr-0 standard 17m
pvc-330cc6ee-6a5f-11e9-a871-080027a851ba 1Gi RWO Delete Bound demo/datadir-mongo-sh-configsvr-1 standard 16m
pvc-3db2d3f5-6a5f-11e9-a871-080027a851ba 1Gi RWO Delete Bound demo/datadir-mongo-sh-configsvr-2 standard 16m
pvc-49b7cc3b-6a5f-11e9-a871-080027a851ba 1Gi RWO Delete Bound demo/datadir-mongo-sh-shard0-0 standard 16m
pvc-5b781770-6a5f-11e9-a871-080027a851ba 1Gi RWO Delete Bound demo/datadir-mongo-sh-shard0-1 standard 15m
pvc-6ba3263e-6a5f-11e9-a871-080027a851ba 1Gi RWO Delete Bound demo/datadir-mongo-sh-shard0-2 standard 15m
pvc-75feb227-6a5f-11e9-a871-080027a851ba 1Gi RWO Delete Bound demo/datadir-mongo-sh-shard1-0 standard 14m
pvc-89bb7bb3-6a5f-11e9-a871-080027a851ba 1Gi RWO Delete Bound demo/datadir-mongo-sh-shard1-1 standard 14m
pvc-98c96ae4-6a5f-11e9-a871-080027a851ba 1Gi RWO Delete Bound demo/datadir-mongo-sh-shard1-2 standard 13m
pvc-a1eebcd2-6a5f-11e9-a871-080027a851ba 1Gi RWO Delete Bound demo/datadir-mongo-sh-shard2-0 standard 13m
pvc-b231fb18-6a5f-11e9-a871-080027a851ba 1Gi RWO Delete Bound demo/datadir-mongo-sh-shard2-1 standard 13m
pvc-c5bb265f-6a5f-11e9-a871-080027a851ba 1Gi RWO Delete Bound demo/datadir-mongo-sh-shard2-2 standard 12m
Services created for MongoDB mongo-sh
$ kubectl get svc -n demo
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
mongo-sh ClusterIP 10.108.188.201 <none> 27017/TCP 18m
mongo-sh-configsvr-gvr ClusterIP None <none> 27017/TCP 18m
mongo-sh-shard0-gvr ClusterIP None <none> 27017/TCP 18m
mongo-sh-shard1-gvr ClusterIP None <none> 27017/TCP 18m
mongo-sh-shard2-gvr ClusterIP None <none> 27017/TCP 18m
KubeDB operator sets the status.phase to Running once the database is successfully created. It has also defaulted some field of crd object. Run the following command to see the modified MongoDB object:
$ kubedb get mg -n demo mongo-sh -o yaml
apiVersion: kubedb.com/v1alpha1
kind: MongoDB
metadata:
creationTimestamp: "2019-04-29T09:13:56Z"
finalizers:
- kubedb.com
generation: 3
name: mongo-sh
namespace: demo
resourceVersion: "25825"
selfLink: /apis/kubedb.com/v1alpha1/namespaces/demo/mongodbs/mongo-sh
uid: 1d83622c-6a5f-11e9-a871-080027a851ba
spec:
certificateSecret:
secretName: mongo-sh-keyfile
databaseSecret:
secretName: mongo-sh-auth
serviceTemplate:
metadata: {}
spec: {}
shardTopology:
configServer:
podTemplate:
controller: {}
metadata: {}
spec:
livenessProbe:
exec:
command:
- mongo
- --eval
- db.adminCommand('ping')
failureThreshold: 3
periodSeconds: 10
successThreshold: 1
timeoutSeconds: 5
readinessProbe:
exec:
command:
- mongo
- --eval
- db.adminCommand('ping')
failureThreshold: 3
periodSeconds: 10
successThreshold: 1
timeoutSeconds: 1
resources: {}
securityContext:
fsGroup: 999
runAsNonRoot: true
runAsUser: 999
replicas: 3
storage:
dataSource: null
resources:
requests:
storage: 1Gi
storageClassName: standard
mongos:
podTemplate:
controller: {}
metadata: {}
spec:
livenessProbe:
exec:
command:
- mongo
- --eval
- db.adminCommand('ping')
failureThreshold: 3
periodSeconds: 10
successThreshold: 1
timeoutSeconds: 5
readinessProbe:
exec:
command:
- mongo
- --eval
- db.adminCommand('ping')
failureThreshold: 3
periodSeconds: 10
successThreshold: 1
timeoutSeconds: 1
resources: {}
securityContext:
fsGroup: 999
runAsNonRoot: true
runAsUser: 999
replicas: 2
strategy:
type: RollingUpdate
shard:
podTemplate:
controller: {}
metadata: {}
spec:
livenessProbe:
exec:
command:
- mongo
- --eval
- db.adminCommand('ping')
failureThreshold: 3
periodSeconds: 10
successThreshold: 1
timeoutSeconds: 5
readinessProbe:
exec:
command:
- mongo
- --eval
- db.adminCommand('ping')
failureThreshold: 3
periodSeconds: 10
successThreshold: 1
timeoutSeconds: 1
resources: {}
securityContext:
fsGroup: 999
runAsNonRoot: true
runAsUser: 999
replicas: 3
shards: 3
storage:
dataSource: null
resources:
requests:
storage: 1Gi
storageClassName: standard
storageType: Durable
terminationPolicy: Pause
updateStrategy:
type: RollingUpdate
version: 3.6-v3
status:
observedGeneration: 3$4212299729528774793
phase: Running
Please note that KubeDB operator has created a new Secret called mongo-sh-auth (format: {mongodb-object-name}-auth) for storing the password for mongodb superuser. This secret contains a username key which contains the username for MongoDB superuser and a password key which contains the password for MongoDB superuser.
If you want to use custom or existing secret please specify that when creating the MongoDB object using spec.databaseSecret.secretName. While creating this secret manually, make sure the secret contains these two keys containing data username and password. For more details, please see here.
Connection Information
Hostname/address: you can use any of these
- Service:
mongo-sh.demo - Pod IP: (
$ kubectl get po -n demo -l mongodb.kubedb.com/node.mongos=mongo-sh-mongos -o yaml | grep podIP)
- Service:
Port:
27017Username: Run following command to get username,
$ kubectl get secrets -n demo mongo-sh-auth -o jsonpath='{.data.\username}' | base64 -d rootPassword: Run the following command to get password,
$ kubectl get secrets -n demo mongo-sh-auth -o jsonpath='{.data.\password}' | base64 -d 7QiqLcuSCmZ8PU5a
Now, you can connect to this database through mongo-shell.
Sharded Data
In this tutorial, we will insert sharded and unsharded document, and we will see if the data actually sharded across cluster or not.
$ kubectl get po -n demo -l mongodb.kubedb.com/node.mongos=mongo-sh-mongos
NAME READY STATUS RESTARTS AGE
mongo-sh-mongos-69b557f9f5-2kz68 1/1 Running 0 49m
mongo-sh-mongos-69b557f9f5-5hvh2 1/1 Running 0 49m
$ kubectl exec -it mongo-sh-mongos-69b557f9f5-2kz68 -n demo bash
mongodb@mongo-sh-mongos-69b557f9f5-2kz68:/$ mongo admin -u root -p 7QiqLcuSCmZ8PU5a
MongoDB shell version v3.6.12
connecting to: mongodb://127.0.0.1:27017/admin?gssapiServiceName=mongodb
Implicit session: session { "id" : UUID("8b7abf57-09e4-4e30-b4a0-a37ebf065e8f") }
MongoDB server version: 3.6.12
Welcome to the MongoDB shell.
For interactive help, type "help".
For more comprehensive documentation, see
http://docs.mongodb.org/
Questions? Try the support group
http://groups.google.com/group/mongodb-user
2019-04-29T10:09:17.311+0000 I STORAGE [main] In File::open(), ::open for '/home/mongodb/.mongorc.js' failed with No such file or directory
mongos> isMaster;
2019-04-29T10:11:16.128+0000 E QUERY [thread1] ReferenceError: isMaster is not defined :
@(shell):1:1
mongos> isMaster();
2019-04-29T10:11:20.020+0000 E QUERY [thread1] ReferenceError: isMaster is not defined :
@(shell):1:1
mongos>
To detect if the MongoDB instance that your client is connected to is mongos, use the isMaster command. When a client connects to a mongos, isMaster returns a document with a msg field that holds the string isdbgrid.
mongos> rs.isMaster()
{
"ismaster" : true,
"msg" : "isdbgrid",
"maxBsonObjectSize" : 16777216,
"maxMessageSizeBytes" : 48000000,
"maxWriteBatchSize" : 100000,
"localTime" : ISODate("2019-04-29T10:12:00.145Z"),
"logicalSessionTimeoutMinutes" : 30,
"maxWireVersion" : 6,
"minWireVersion" : 0,
"ok" : 1,
"operationTime" : Timestamp(1556532710, 1),
"$clusterTime" : {
"clusterTime" : Timestamp(1556532710, 1),
"signature" : {
"hash" : BinData(0,"6W7pmWBdVSzY0x+BxQj74d0WhXg="),
"keyId" : NumberLong("6685242219722440730")
}
}
}
mongo-sh Shard status,
mongos> sh.status()
--- Sharding Status ---
sharding version: {
"_id" : 1,
"minCompatibleVersion" : 5,
"currentVersion" : 6,
"clusterId" : ObjectId("5cc6c061f439d076e04d737b")
}
shards:
{ "_id" : "shard0", "host" : "shard0/mongo-sh-shard0-0.mongo-sh-shard0-gvr.demo.svc.cluster.local:27017,mongo-sh-shard0-1.mongo-sh-shard0-gvr.demo.svc.cluster.local:27017,mongo-sh-shard0-2.mongo-sh-shard0-gvr.demo.svc.cluster.local:27017", "state" : 1 }
{ "_id" : "shard1", "host" : "shard1/mongo-sh-shard1-0.mongo-sh-shard1-gvr.demo.svc.cluster.local:27017,mongo-sh-shard1-1.mongo-sh-shard1-gvr.demo.svc.cluster.local:27017,mongo-sh-shard1-2.mongo-sh-shard1-gvr.demo.svc.cluster.local:27017", "state" : 1 }
{ "_id" : "shard2", "host" : "shard2/mongo-sh-shard2-0.mongo-sh-shard2-gvr.demo.svc.cluster.local:27017,mongo-sh-shard2-1.mongo-sh-shard2-gvr.demo.svc.cluster.local:27017,mongo-sh-shard2-2.mongo-sh-shard2-gvr.demo.svc.cluster.local:27017", "state" : 1 }
active mongoses:
"3.6.12" : 2
autosplit:
Currently enabled: yes
balancer:
Currently enabled: yes
Currently running: no
Failed balancer rounds in last 5 attempts: 0
Migration Results for the last 24 hours:
No recent migrations
databases:
{ "_id" : "config", "primary" : "config", "partitioned" : true }
config.system.sessions
shard key: { "_id" : 1 }
unique: false
balancing: true
chunks:
shard0 1
{ "_id" : { "$minKey" : 1 } } -->> { "_id" : { "$maxKey" : 1 } } on : shard0 Timestamp(1, 0)
Shard collection test.testcoll and insert document. See sh.shardCollection(namespace, key, unique, options) for details about shardCollection command.
mongos> sh.enableSharding("test");
{
"ok" : 1,
"operationTime" : Timestamp(1556535000, 8),
"$clusterTime" : {
"clusterTime" : Timestamp(1556535000, 8),
"signature" : {
"hash" : BinData(0,"84KefOzN8tKmsPfr6IrnBUxF9NM="),
"keyId" : NumberLong("6685242219722440730")
}
}
}
mongos> sh.shardCollection("test.testcoll", {"myfield": 1});
{
"collectionsharded" : "test.testcoll",
"collectionUUID" : UUID("68ff9452-40bb-41a2-b35a-405132f90cd3"),
"ok" : 1,
"operationTime" : Timestamp(1556535010, 8),
"$clusterTime" : {
"clusterTime" : Timestamp(1556535010, 8),
"signature" : {
"hash" : BinData(0,"IgVzMa8qE4UBzjc2gOZJX5kZ3T4="),
"keyId" : NumberLong("6685242219722440730")
}
}
}
mongos> use test;
switched to db test
mongos> db.testcoll.insert({"myfield": "a", "otherfield": "b"});
WriteResult({ "nInserted" : 1 })
mongos> db.testcoll.insert({"myfield": "c", "otherfield": "d", "kube" : "db" });
WriteResult({ "nInserted" : 1 })
mongos> db.testcoll.find();
{ "_id" : ObjectId("5cc6d6f656a9ddd30be2c12a"), "myfield" : "a", "otherfield" : "b" }
{ "_id" : ObjectId("5cc6d71e56a9ddd30be2c12b"), "myfield" : "c", "otherfield" : "d", "kube" : "db" }
Run sh.status() to see whether the test database has sharding enabled, and the primary shard for the test database.
The Sharded Collection section sh.status.databases.<collection> provides information on the sharding details for sharded collection(s) (E.g. test.testcoll). For each sharded collection, the section displays the shard key, the number of chunks per shard(s), the distribution of documents across chunks, and the tag information, if any, for shard key range(s).
mongos> sh.status();
--- Sharding Status ---
sharding version: {
"_id" : 1,
"minCompatibleVersion" : 5,
"currentVersion" : 6,
"clusterId" : ObjectId("5cc6c061f439d076e04d737b")
}
shards:
{ "_id" : "shard0", "host" : "shard0/mongo-sh-shard0-0.mongo-sh-shard0-gvr.demo.svc.cluster.local:27017,mongo-sh-shard0-1.mongo-sh-shard0-gvr.demo.svc.cluster.local:27017,mongo-sh-shard0-2.mongo-sh-shard0-gvr.demo.svc.cluster.local:27017", "state" : 1 }
{ "_id" : "shard1", "host" : "shard1/mongo-sh-shard1-0.mongo-sh-shard1-gvr.demo.svc.cluster.local:27017,mongo-sh-shard1-1.mongo-sh-shard1-gvr.demo.svc.cluster.local:27017,mongo-sh-shard1-2.mongo-sh-shard1-gvr.demo.svc.cluster.local:27017", "state" : 1 }
{ "_id" : "shard2", "host" : "shard2/mongo-sh-shard2-0.mongo-sh-shard2-gvr.demo.svc.cluster.local:27017,mongo-sh-shard2-1.mongo-sh-shard2-gvr.demo.svc.cluster.local:27017,mongo-sh-shard2-2.mongo-sh-shard2-gvr.demo.svc.cluster.local:27017", "state" : 1 }
active mongoses:
"3.6.12" : 2
autosplit:
Currently enabled: yes
balancer:
Currently enabled: yes
Currently running: no
Failed balancer rounds in last 5 attempts: 0
Migration Results for the last 24 hours:
No recent migrations
databases:
{ "_id" : "config", "primary" : "config", "partitioned" : true }
config.system.sessions
shard key: { "_id" : 1 }
unique: false
balancing: true
chunks:
shard0 1
{ "_id" : { "$minKey" : 1 } } -->> { "_id" : { "$maxKey" : 1 } } on : shard0 Timestamp(1, 0)
{ "_id" : "test", "primary" : "shard1", "partitioned" : true }
test.testcoll
shard key: { "myfield" : 1 }
unique: false
balancing: true
chunks:
shard1 1
{ "myfield" : { "$minKey" : 1 } } -->> { "myfield" : { "$maxKey" : 1 } } on : shard1 Timestamp(1, 0)
Now create another database where partiotioned is not applied and see how the data is stored.
mongos> use demo
switched to db demo
mongos> db.testcoll2.insert({"myfield": "ccc", "otherfield": "d", "kube" : "db" });
WriteResult({ "nInserted" : 1 })
mongos> db.testcoll2.insert({"myfield": "aaa", "otherfield": "d", "kube" : "db" });
WriteResult({ "nInserted" : 1 })
mongos> db.testcoll2.find()
{ "_id" : ObjectId("5cc6dc831b6d9b3cddc947ec"), "myfield" : "ccc", "otherfield" : "d", "kube" : "db" }
{ "_id" : ObjectId("5cc6dce71b6d9b3cddc947ed"), "myfield" : "aaa", "otherfield" : "d", "kube" : "db" }
Now, eventually sh.status()
mongos> sh.status()
--- Sharding Status ---
sharding version: {
"_id" : 1,
"minCompatibleVersion" : 5,
"currentVersion" : 6,
"clusterId" : ObjectId("5cc6c061f439d076e04d737b")
}
shards:
{ "_id" : "shard0", "host" : "shard0/mongo-sh-shard0-0.mongo-sh-shard0-gvr.demo.svc.cluster.local:27017,mongo-sh-shard0-1.mongo-sh-shard0-gvr.demo.svc.cluster.local:27017,mongo-sh-shard0-2.mongo-sh-shard0-gvr.demo.svc.cluster.local:27017", "state" : 1 }
{ "_id" : "shard1", "host" : "shard1/mongo-sh-shard1-0.mongo-sh-shard1-gvr.demo.svc.cluster.local:27017,mongo-sh-shard1-1.mongo-sh-shard1-gvr.demo.svc.cluster.local:27017,mongo-sh-shard1-2.mongo-sh-shard1-gvr.demo.svc.cluster.local:27017", "state" : 1 }
{ "_id" : "shard2", "host" : "shard2/mongo-sh-shard2-0.mongo-sh-shard2-gvr.demo.svc.cluster.local:27017,mongo-sh-shard2-1.mongo-sh-shard2-gvr.demo.svc.cluster.local:27017,mongo-sh-shard2-2.mongo-sh-shard2-gvr.demo.svc.cluster.local:27017", "state" : 1 }
active mongoses:
"3.6.12" : 2
autosplit:
Currently enabled: yes
balancer:
Currently enabled: yes
Currently running: no
Failed balancer rounds in last 5 attempts: 0
Migration Results for the last 24 hours:
No recent migrations
databases:
{ "_id" : "config", "primary" : "config", "partitioned" : true }
config.system.sessions
shard key: { "_id" : 1 }
unique: false
balancing: true
chunks:
shard0 1
{ "_id" : { "$minKey" : 1 } } -->> { "_id" : { "$maxKey" : 1 } } on : shard0 Timestamp(1, 0)
{ "_id" : "demo", "primary" : "shard2", "partitioned" : false }
{ "_id" : "test", "primary" : "shard1", "partitioned" : true }
test.testcoll
shard key: { "myfield" : 1 }
unique: false
balancing: true
chunks:
shard1 1
{ "myfield" : { "$minKey" : 1 } } -->> { "myfield" : { "$maxKey" : 1 } } on : shard1 Timestamp(1, 0)
Here, demo database is not partitioned and all collections under demo database are stored in it’s primary shard, which is shard2.
Update number of ShardTopology Instances
User can increase or decrease the number of router/mongos spec.shardTopology.mongos.replicas.
At this moment, decreasing the number of shards and replicasets is not handled from KubeDB end. But, User can increase the number of instances if needed.
Here a table of allowed actions are given for mongodb ShardTopology,
| Instances | Increase | Decrease |
|---|---|---|
# of replicas of Mongos spec.shardTopology.mongos.replicas | ✓ | ✓ |
# of Shards spec.shardTopology.shard.shards | ✓ | ✗ |
# of replicaset of each Shard spec.shardTopology.shard.replicas | ✓ | ✗ |
# of replicaset of ConfigServer spec.shardTopology.configServer.replicas | ✓ | ✗ |
Now edit MongoDB mongo-sh to increase spec.shardTopology.shard.shards to 4 and increase spec.shardTopology.mongos to 3.
$ kubectl edit mg -n demo mongo-sh
apiVersion: kubedb.com/v1alpha1
kind: MongoDB
metadata:
name: mongo-sh
namespace: demo
...
spec:
shardTopology:
mongos:
replicas: 3 # set 3
...
shard:
shards: 4 # set 4
...
...
Watch for pod changes,
$ kubectl get po --all-namespaces -w
NAMESPACE NAME READY STATUS RESTARTS AGE
demo mongo-sh-configsvr-0 1/1 Running 0 8m12s
demo mongo-sh-configsvr-1 1/1 Running 0 7m41s
demo mongo-sh-configsvr-2 1/1 Running 0 7m17s
demo mongo-sh-mongos-69b557f9f5-2qvb7 1/1 Running 0 3m44s
demo mongo-sh-mongos-69b557f9f5-6z2s4 1/1 Running 0 3m44s
demo mongo-sh-shard0-0 1/1 Running 0 7m4s
demo mongo-sh-shard0-1 1/1 Running 0 6m37s
demo mongo-sh-shard0-2 1/1 Running 0 6m20s
demo mongo-sh-shard1-0 1/1 Running 0 5m55s
demo mongo-sh-shard1-1 1/1 Running 0 5m29s
demo mongo-sh-shard1-2 1/1 Running 0 5m14s
demo mongo-sh-shard2-0 1/1 Running 0 4m59s
demo mongo-sh-shard2-1 1/1 Running 0 4m32s
demo mongo-sh-shard2-2 1/1 Running 0 4m11s
kube-system coredns-fb8b8dccf-nzb5q 1/1 Running 1 165m
kube-system coredns-fb8b8dccf-tqldv 1/1 Running 1 165m
kube-system etcd-minikube 1/1 Running 0 164m
kube-system kube-addon-manager-minikube 1/1 Running 0 164m
kube-system kube-apiserver-minikube 1/1 Running 0 163m
kube-system kube-controller-manager-minikube 1/1 Running 0 164m
kube-system kube-proxy-qznbv 1/1 Running 0 165m
kube-system kube-scheduler-minikube 1/1 Running 0 163m
kube-system kubedb-operator-c8cd5c69-c5nkc 1/1 Running 0 44m
kube-system kubernetes-dashboard-79dd6bfc48-l88rk 1/1 Running 4 165m
kube-system storage-provisioner 1/1 Running 0 164m
demo mongo-sh-shard3-0 0/1 Pending 0 0s
demo mongo-sh-shard3-0 0/1 Pending 0 0s
demo mongo-sh-shard3-0 0/1 Pending 0 9s
demo mongo-sh-shard3-0 0/1 Init:0/2 0 9s
demo mongo-sh-shard3-0 0/1 Init:1/2 0 10s
demo mongo-sh-shard3-0 0/1 Init:1/2 0 11s
demo mongo-sh-shard3-0 0/1 PodInitializing 0 30s
demo mongo-sh-shard3-0 0/1 Running 0 31s
demo mongo-sh-shard3-0 1/1 Running 0 41s
demo mongo-sh-shard3-1 0/1 Pending 0 0s
demo mongo-sh-shard3-1 0/1 Pending 0 0s
demo mongo-sh-shard3-1 0/1 Pending 0 5s
demo mongo-sh-shard3-1 0/1 Init:0/2 0 5s
demo mongo-sh-shard3-1 0/1 Init:1/2 0 6s
demo mongo-sh-shard3-1 0/1 Init:1/2 0 7s
demo mongo-sh-shard3-1 0/1 PodInitializing 0 15s
demo mongo-sh-shard3-1 0/1 Running 0 16s
demo mongo-sh-shard3-1 1/1 Running 0 23s
demo mongo-sh-shard3-2 0/1 Pending 0 0s
demo mongo-sh-shard3-2 0/1 Pending 0 0s
demo mongo-sh-shard3-2 0/1 Pending 0 2s
demo mongo-sh-shard3-2 0/1 Init:0/2 0 2s
demo mongo-sh-shard3-2 0/1 Init:1/2 0 4s
demo mongo-sh-shard3-2 0/1 Init:1/2 0 5s
demo mongo-sh-shard3-2 0/1 PodInitializing 0 14s
demo mongo-sh-shard3-2 0/1 Running 0 15s
demo mongo-sh-shard3-2 1/1 Running 0 22s
demo mongo-sh-mongos-69b557f9f5-w77cs 0/1 Pending 0 0s
demo mongo-sh-mongos-69b557f9f5-w77cs 0/1 Pending 0 0s
demo mongo-sh-mongos-69b557f9f5-w77cs 0/1 Init:0/2 0 0s
demo mongo-sh-mongos-598658d8f9-6j544 0/1 Pending 0 0s
demo mongo-sh-mongos-598658d8f9-6j544 0/1 Pending 0 0s
demo mongo-sh-mongos-598658d8f9-6j544 0/1 Init:0/2 0 0s
demo mongo-sh-mongos-69b557f9f5-w77cs 0/1 Init:0/2 0 1s
demo mongo-sh-mongos-69b557f9f5-w77cs 0/1 Init:1/2 0 3s
demo mongo-sh-mongos-598658d8f9-6j544 0/1 Init:1/2 0 3s
demo mongo-sh-mongos-598658d8f9-6j544 0/1 Init:1/2 0 4s
demo mongo-sh-mongos-69b557f9f5-w77cs 0/1 Init:1/2 0 4s
demo mongo-sh-mongos-69b557f9f5-w77cs 0/1 PodInitializing 0 7s
demo mongo-sh-mongos-69b557f9f5-w77cs 0/1 Running 0 8s
demo mongo-sh-mongos-598658d8f9-6j544 0/1 PodInitializing 0 8s
demo mongo-sh-mongos-598658d8f9-6j544 0/1 Running 0 9s
demo mongo-sh-mongos-598658d8f9-6j544 1/1 Running 0 12s
demo mongo-sh-mongos-69b557f9f5-w77cs 0/1 Terminating 0 12s
demo mongo-sh-mongos-598658d8f9-tmwvb 0/1 Pending 0 0s
demo mongo-sh-mongos-598658d8f9-tmwvb 0/1 Pending 0 1s
demo mongo-sh-mongos-598658d8f9-tmwvb 0/1 Init:0/2 0 1s
demo mongo-sh-mongos-598658d8f9-tmwvb 0/1 Init:1/2 0 3s
demo mongo-sh-mongos-69b557f9f5-w77cs 0/1 Terminating 0 15s
demo mongo-sh-mongos-598658d8f9-tmwvb 0/1 Init:1/2 0 4s
demo mongo-sh-mongos-69b557f9f5-w77cs 0/1 Terminating 0 19s
demo mongo-sh-mongos-69b557f9f5-w77cs 0/1 Terminating 0 19s
demo mongo-sh-mongos-598658d8f9-tmwvb 0/1 PodInitializing 0 7s
demo mongo-sh-mongos-598658d8f9-tmwvb 0/1 Running 0 8s
demo mongo-sh-mongos-598658d8f9-tmwvb 1/1 Running 0 10s
demo mongo-sh-mongos-69b557f9f5-6z2s4 1/1 Terminating 0 6m6s
demo mongo-sh-mongos-598658d8f9-464xr 0/1 Pending 0 0s
demo mongo-sh-mongos-598658d8f9-464xr 0/1 Pending 0 0s
demo mongo-sh-mongos-598658d8f9-464xr 0/1 Init:0/2 0 0s
demo mongo-sh-mongos-69b557f9f5-6z2s4 0/1 Terminating 0 6m7s
demo mongo-sh-mongos-598658d8f9-464xr 0/1 Init:1/2 0 2s
demo mongo-sh-mongos-598658d8f9-464xr 0/1 Init:1/2 0 3s
demo mongo-sh-mongos-598658d8f9-464xr 0/1 PodInitializing 0 6s
demo mongo-sh-mongos-69b557f9f5-6z2s4 0/1 Terminating 0 6m13s
demo mongo-sh-mongos-69b557f9f5-6z2s4 0/1 Terminating 0 6m13s
demo mongo-sh-mongos-598658d8f9-464xr 0/1 Running 0 7s
demo mongo-sh-mongos-598658d8f9-464xr 1/1 Running 0 14s
demo mongo-sh-mongos-69b557f9f5-2qvb7 1/1 Terminating 0 6m21s
demo mongo-sh-mongos-69b557f9f5-2qvb7 0/1 Terminating 0 6m22s
demo mongo-sh-mongos-69b557f9f5-2qvb7 0/1 Terminating 0 6m23s
demo mongo-sh-mongos-69b557f9f5-2qvb7 0/1 Terminating 0 6m23s
You can see that an extra statefulset mongo-sh-shard3 is created as 4th shard and one extra mongos instance also came up.
Notice that, all new mongos instances came up replacing old instances because of some changes in shard config. This update strategy follows spec.shardTopology.mongos.strategy, which is optional. If not provided, kubernetes will use default deploymentStrategy, ie. RollingUpdate. See more about Deployment Strategy.
$ kubectl get deploy -n demo -w
NAME READY UP-TO-DATE AVAILABLE AGE
mongo-sh-mongos 2/2 2 2 12m
mongo-sh-mongos 2/3 2 2 13m
mongo-sh-mongos 2/3 2 2 13m
mongo-sh-mongos 2/3 2 2 13m
mongo-sh-mongos 2/3 3 2 13m
mongo-sh-mongos 3/3 3 3 13m
Now check sh.status() in mongos,
$ kubectl get po -n demo -l mongodb.kubedb.com/node.mongos=mongo-sh-mongos
NAME READY STATUS RESTARTS AGE
mongo-sh-mongos-598658d8f9-6j544 1/1 Running 0 17m
mongo-sh-mongos-598658d8f9-s8gn4 1/1 Running 0 9m54s
mongo-sh-mongos-598658d8f9-tmwvb 1/1 Running 0 16m
$ kubectl exec -it mongo-sh-mongos-598658d8f9-6j544 -n demo bash
mongodb@mongo-sh-mongos-598658d8f9-6j544:/$ mongo admin -u root -p 7QiqLcuSCmZ8PU5a
mongos> sh.status()
--- Sharding Status ---
sharding version: {
"_id" : 1,
"minCompatibleVersion" : 5,
"currentVersion" : 6,
"clusterId" : ObjectId("5cc7ed91d06f28b1b3c64c66")
}
shards:
{ "_id" : "shard0", "host" : "shard0/mongo-sh-shard0-0.mongo-sh-shard0-gvr.demo.svc.cluster.local:27017,mongo-sh-shard0-1.mongo-sh-shard0-gvr.demo.svc.cluster.local:27017,mongo-sh-shard0-2.mongo-sh-shard0-gvr.demo.svc.cluster.local:27017", "state" : 1 }
{ "_id" : "shard1", "host" : "shard1/mongo-sh-shard1-0.mongo-sh-shard1-gvr.demo.svc.cluster.local:27017,mongo-sh-shard1-1.mongo-sh-shard1-gvr.demo.svc.cluster.local:27017,mongo-sh-shard1-2.mongo-sh-shard1-gvr.demo.svc.cluster.local:27017", "state" : 1 }
{ "_id" : "shard2", "host" : "shard2/mongo-sh-shard2-0.mongo-sh-shard2-gvr.demo.svc.cluster.local:27017,mongo-sh-shard2-1.mongo-sh-shard2-gvr.demo.svc.cluster.local:27017,mongo-sh-shard2-2.mongo-sh-shard2-gvr.demo.svc.cluster.local:27017", "state" : 1 }
{ "_id" : "shard3", "host" : "shard3/mongo-sh-shard3-0.mongo-sh-shard3-gvr.demo.svc.cluster.local:27017,mongo-sh-shard3-1.mongo-sh-shard3-gvr.demo.svc.cluster.local:27017,mongo-sh-shard3-2.mongo-sh-shard3-gvr.demo.svc.cluster.local:27017", "state" : 1 }
active mongoses:
"3.6.12" : 3
autosplit:
Currently enabled: yes
balancer:
Currently enabled: yes
Currently running: no
Failed balancer rounds in last 5 attempts: 0
Migration Results for the last 24 hours:
No recent migrations
databases:
{ "_id" : "config", "primary" : "config", "partitioned" : true }
config.system.sessions
shard key: { "_id" : 1 }
unique: false
balancing: true
chunks:
shard0 1
{ "_id" : { "$minKey" : 1 } } -->> { "_id" : { "$maxKey" : 1 } } on : shard0 Timestamp(1, 0)
{ "_id" : "demo", "primary" : "shard2", "partitioned" : false }
{ "_id" : "test", "primary" : "shard1", "partitioned" : true }
test.testcoll
shard key: { "myfield" : 1 }
unique: false
balancing: true
chunks:
shard1 1
{ "myfield" : { "$minKey" : 1 } } -->> { "myfield" : { "$maxKey" : 1 } } on : shard1 Timestamp(1, 0)
Pause Database
When, terminationPolicy is DoNotTerminate, KubeDB takes advantage of ValidationWebhook feature in Kubernetes 1.9.0 or later clusters to implement DoNotTerminate feature. If admission webhook is enabled, It prevents users from deleting the database as long as the spec.terminationPolicy is set to DoNotTerminate.
Since the MongoDB object created in this tutorial has spec.terminationPolicy set to Pause (default), if you delete the MongoDB object, KubeDB operator will create a dormant database while deleting the StatefulSet and its pods but leaves the PVCs unchanged.
$ kubedb delete mg mongo-sh -n demo
mongodb.kubedb.com "mongo-sh" deleted
$ kubedb get drmn -n demo mongo-sh
NAME STATUS AGE
mongo-sh Pausing 13s
$ kubedb get drmn -n demo mongo-sh
NAME STATUS AGE
mongo-sh Paused 52s
$ kubedb get drmn -n demo mongo-sh -o yaml
apiVersion: kubedb.com/v1alpha1
kind: DormantDatabase
metadata:
creationTimestamp: "2019-04-29T11:24:24Z"
finalizers:
- kubedb.com
generation: 1
labels:
kubedb.com/kind: MongoDB
name: mongo-sh
namespace: demo
resourceVersion: "35082"
selfLink: /apis/kubedb.com/v1alpha1/namespaces/demo/dormantdatabases/mongo-sh
uid: 579c2c2d-6a71-11e9-a871-080027a851ba
spec:
origin:
metadata:
creationTimestamp: "2019-04-29T09:13:56Z"
name: mongo-sh
namespace: demo
spec:
mongodb:
certificateSecret:
secretName: mongo-sh-keyfile
databaseSecret:
secretName: mongo-sh-auth
serviceTemplate:
metadata: {}
spec: {}
shardTopology:
configServer:
podTemplate:
controller: {}
metadata: {}
spec:
livenessProbe:
exec:
command:
- mongo
- --eval
- db.adminCommand('ping')
failureThreshold: 3
periodSeconds: 10
successThreshold: 1
timeoutSeconds: 5
readinessProbe:
exec:
command:
- mongo
- --eval
- db.adminCommand('ping')
failureThreshold: 3
periodSeconds: 10
successThreshold: 1
timeoutSeconds: 1
resources: {}
securityContext:
fsGroup: 999
runAsNonRoot: true
runAsUser: 999
replicas: 3
storage:
dataSource: null
resources:
requests:
storage: 1Gi
storageClassName: standard
mongos:
podTemplate:
controller: {}
metadata: {}
spec:
livenessProbe:
exec:
command:
- mongo
- --eval
- db.adminCommand('ping')
failureThreshold: 3
periodSeconds: 10
successThreshold: 1
timeoutSeconds: 5
readinessProbe:
exec:
command:
- mongo
- --eval
- db.adminCommand('ping')
failureThreshold: 3
periodSeconds: 10
successThreshold: 1
timeoutSeconds: 1
resources: {}
securityContext:
fsGroup: 999
runAsNonRoot: true
runAsUser: 999
replicas: 2
strategy:
type: RollingUpdate
shard:
podTemplate:
controller: {}
metadata: {}
spec:
livenessProbe:
exec:
command:
- mongo
- --eval
- db.adminCommand('ping')
failureThreshold: 3
periodSeconds: 10
successThreshold: 1
timeoutSeconds: 5
readinessProbe:
exec:
command:
- mongo
- --eval
- db.adminCommand('ping')
failureThreshold: 3
periodSeconds: 10
successThreshold: 1
timeoutSeconds: 1
resources: {}
securityContext:
fsGroup: 999
runAsNonRoot: true
runAsUser: 999
replicas: 3
shards: 3
storage:
dataSource: null
resources:
requests:
storage: 1Gi
storageClassName: standard
storageType: Durable
terminationPolicy: Pause
updateStrategy:
type: RollingUpdate
version: 3.6-v3
status:
observedGeneration: 1$16440556888999634490
pausingTime: "2019-04-29T11:24:41Z"
phase: Paused
Here,
spec.originis the spec of the original spec of the original MongoDB object.status.phasepoints to the current database statePaused.
Resume Dormant Database
To resume the database from the dormant state, create same MongoDB object with same Spec.
In this tutorial, the dormant database can be resumed by creating original MongoDB object.
The below command will resume the DormantDatabase mongo-sh.
$ kubectl create -f https://github.com/kubedb/docs/raw/v0.13.0-rc.0/docs/examples/mongodb/clustering/mongo-sh.yaml
mongodb.kubedb.com/mongo-sh created
$ kubectl get mg -n demo
NAME VERSION STATUS AGE
mongo-sh 3.6-v3 Running 6m27s
Now, If you again exec into pod and look for previous data, you will see that, all the data persists.
$ kubectl get po -n demo -l mongodb.kubedb.com/node.mongos=mongo-sh-mongos
NAME READY STATUS RESTARTS AGE
mongo-sh-mongos-69b557f9f5-62j76 1/1 Running 0 3m52s
mongo-sh-mongos-69b557f9f5-tdn69 1/1 Running 0 3m52s
$ kubectl exec -it mongo-sh-mongos-69b557f9f5-62j76 -n demo bash
mongodb@mongo-sh-mongos-69b557f9f5-62j76:/$ mongo admin -u root -p 7QiqLcuSCmZ8PU5a
mongos> use test;
switched to db test
mongos> db.testcoll.find();
{ "_id" : ObjectId("5cc6d6f656a9ddd30be2c12a"), "myfield" : "a", "otherfield" : "b" }
{ "_id" : ObjectId("5cc6d71e56a9ddd30be2c12b"), "myfield" : "c", "otherfield" : "d", "kube" : "db" }
mongos> sh.status()
--- Sharding Status ---
sharding version: {
"_id" : 1,
"minCompatibleVersion" : 5,
"currentVersion" : 6,
"clusterId" : ObjectId("5cc6c061f439d076e04d737b")
}
shards:
{ "_id" : "shard0", "host" : "shard0/mongo-sh-shard0-0.mongo-sh-shard0-gvr.demo.svc.cluster.local:27017,mongo-sh-shard0-1.mongo-sh-shard0-gvr.demo.svc.cluster.local:27017,mongo-sh-shard0-2.mongo-sh-shard0-gvr.demo.svc.cluster.local:27017", "state" : 1 }
{ "_id" : "shard1", "host" : "shard1/mongo-sh-shard1-0.mongo-sh-shard1-gvr.demo.svc.cluster.local:27017,mongo-sh-shard1-1.mongo-sh-shard1-gvr.demo.svc.cluster.local:27017,mongo-sh-shard1-2.mongo-sh-shard1-gvr.demo.svc.cluster.local:27017", "state" : 1 }
{ "_id" : "shard2", "host" : "shard2/mongo-sh-shard2-0.mongo-sh-shard2-gvr.demo.svc.cluster.local:27017,mongo-sh-shard2-1.mongo-sh-shard2-gvr.demo.svc.cluster.local:27017,mongo-sh-shard2-2.mongo-sh-shard2-gvr.demo.svc.cluster.local:27017", "state" : 1 }
active mongoses:
"3.6.12" : 2
autosplit:
Currently enabled: yes
balancer:
Currently enabled: yes
Currently running: no
Failed balancer rounds in last 5 attempts: 5
Last reported error: Could not find host matching read preference { mode: "primary" } for set shard2
Time of Reported error: Mon Apr 29 2019 11:30:33 GMT+0000 (UTC)
Migration Results for the last 24 hours:
No recent migrations
databases:
{ "_id" : "config", "primary" : "config", "partitioned" : true }
config.system.sessions
shard key: { "_id" : 1 }
unique: false
balancing: true
chunks:
shard0 1
{ "_id" : { "$minKey" : 1 } } -->> { "_id" : { "$maxKey" : 1 } } on : shard0 Timestamp(1, 0)
{ "_id" : "demo", "primary" : "shard2", "partitioned" : false }
{ "_id" : "test", "primary" : "shard1", "partitioned" : true }
test.testcoll
shard key: { "myfield" : 1 }
unique: false
balancing: true
chunks:
shard1 1
{ "myfield" : { "$minKey" : 1 } } -->> { "myfield" : { "$maxKey" : 1 } } on : shard1 Timestamp(1, 0)
WipeOut DormantDatabase
You can wipe out a DormantDatabase while deleting the object by setting spec.wipeOut to true. KubeDB operator will delete any relevant resources of this MongoDB database (i.e, PVCs, Secrets, Snapshots). It will also delete snapshot data stored in the Cloud Storage buckets.
$ kubedb delete mg mongo-sh -n demo
mongodb.kubedb.com "mongo-sh" deleted
$ kubedb edit drmn -n demo mongo-sh
apiVersion: kubedb.com/v1alpha1
kind: DormantDatabase
metadata:
name: mongo-sh
namespace: demo
...
spec:
wipeOut: true
...
status:
phase: Paused
...
If spec.wipeOut is not set to true while deleting the dormantdatabase object, then only this object will be deleted and kubedb-operator won’t delete related Secrets, PVCs, and Snapshots. So, users still can access the stored data in the cloud storage buckets as well as PVCs.
Delete DormantDatabase
As it is already discussed above, DormantDatabase can be deleted with or without wiping out the resources. To delete the dormantdatabase,
$ kubectl delete drmn mongo-sh -n demo
dormantdatabase.kubedb.com "mongo-sh" deleted
Cleaning up
To cleanup the Kubernetes resources created by this tutorial, run:
kubectl patch -n demo mg/mongo-sh -p '{"spec":{"terminationPolicy":"WipeOut"}}' --type="merge"
kubectl delete -n demo mg/mongo-sh
kubectl patch -n demo drmn/mongo-sh -p '{"spec":{"wipeOut":true}}' --type="merge"
kubectl delete -n demo drmn/mongo-sh
kubectl delete ns demo
Next Steps
- Snapshot and Restore process of MongoDB databases using KubeDB.
- Take Scheduled Snapshot of MongoDB databases using KubeDB.
- Initialize MongoDB with Script.
- Initialize MongoDB with Snapshot.
- Monitor your MongoDB database with KubeDB using out-of-the-box CoreOS Prometheus Operator.
- Monitor your MongoDB database with KubeDB using out-of-the-box builtin-Prometheus.
- Use private Docker registry to deploy MongoDB with KubeDB.
- Detail concepts of MongoDB object.
- Detail concepts of MongoDBVersion object.
- Want to hack on KubeDB? Check our contribution guidelines.