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KubeDB - MongoDB ReplicaSet
This tutorial will show you how to use KubeDB to run a MongoDB ReplicaSet.
Before You Begin
Before proceeding:
Read mongodb replication concept to learn about MongoDB Replica Set 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 kind.
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 MongoDB ReplicaSet
To deploy a MongoDB ReplicaSet, user have to specify spec.replicaSet option in Mongodb CRD.
The following is an example of a Mongodb object which creates MongoDB ReplicaSet of three members.
apiVersion: kubedb.com/v1alpha2
kind: MongoDB
metadata:
name: mgo-replicaset
namespace: demo
spec:
version: "4.4.26"
replicas: 3
replicaSet:
name: rs0
storage:
storageClassName: "standard"
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 1Gi
$ kubectl create -f https://github.com/kubedb/docs/raw/v2023.12.21/docs/examples/mongodb/clustering/replicaset.yaml
mongodb.kubedb.com/mgo-replicaset created
Here,
spec.replicaSetrepresents the configuration for replicaset.namedenotes the name of mongodb replicaset.
spec.keyFileSecret(optional) is a secret name that contains keyfile (a random string)againstkey.txtkey. Each mongod instances in the replica set andshardTopologyuses 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 thekeyFileSecretby creating a secret with keykey.txt. See here to create the string forkeyFileSecret. IfkeyFileSecretis not given, KubeDB operator will generate akeyFileSecretitself.spec.replicasdenotes the number of members inrs0mongodb replicaset.spec.storagespecifies the StorageClass of PVC dynamically allocated to store data for this database. This storage spec will be passed to the StatefulSet created by KubeDB operator to run database pods. So, each members will have a pod of this storage configuration. You can specify any StorageClass available in your cluster with appropriate resource requests.
KubeDB operator watches for MongoDB objects using Kubernetes api. When a MongoDB object is created, KubeDB operator will create a new StatefulSet and a Service with the matching MongoDB object name. This service will always point to the primary of the replicaset. KubeDB operator will also create a governing service for StatefulSets with the name <mongodb-name>-pods.
$ kubectl dba describe mg -n demo mgo-replicaset
Name: mgo-replicaset
Namespace: demo
CreationTimestamp: Wed, 10 Feb 2021 11:05:06 +0600
Labels: <none>
Annotations: kubectl.kubernetes.io/last-applied-configuration={"apiVersion":"kubedb.com/v1alpha2","kind":"MongoDB","metadata":{"annotations":{},"name":"mgo-replicaset","namespace":"demo"},"spec":{"replicaSet":{"na...
Replicas: 3 total
Status: Ready
StorageType: Durable
Volume:
StorageClass: standard
Capacity: 1Gi
Access Modes: RWO
Paused: false
Halted: false
Termination Policy: Delete
StatefulSet:
Name: mgo-replicaset
CreationTimestamp: Wed, 10 Feb 2021 11:05:06 +0600
Labels: app.kubernetes.io/component=database
app.kubernetes.io/instance=mgo-replicaset
app.kubernetes.io/managed-by=kubedb.com
app.kubernetes.io/name=mongodbs.kubedb.com
Annotations: <none>
Replicas: 824637635032 desired | 3 total
Pods Status: 3 Running / 0 Waiting / 0 Succeeded / 0 Failed
Service:
Name: mgo-replicaset
Labels: app.kubernetes.io/component=database
app.kubernetes.io/instance=mgo-replicaset
app.kubernetes.io/managed-by=kubedb.com
app.kubernetes.io/name=mongodbs.kubedb.com
Annotations: <none>
Type: ClusterIP
IP: fd00:10:96::d5f5
Port: primary 27017/TCP
TargetPort: db/TCP
Endpoints: [fd00:10:244::a]:27017
Service:
Name: mgo-replicaset-pods
Labels: app.kubernetes.io/component=database
app.kubernetes.io/instance=mgo-replicaset
app.kubernetes.io/managed-by=kubedb.com
app.kubernetes.io/name=mongodbs.kubedb.com
Annotations: <none>
Type: ClusterIP
IP: None
Port: db 27017/TCP
TargetPort: db/TCP
Endpoints: [fd00:10:244::a]:27017,[fd00:10:244::c]:27017,[fd00:10:244::e]:27017
Auth Secret:
Name: mgo-replicaset-auth
Labels: app.kubernetes.io/component=database
app.kubernetes.io/instance=mgo-replicaset
app.kubernetes.io/managed-by=kubedb.com
app.kubernetes.io/name=mongodbs.kubedb.com
Annotations: <none>
Type: Opaque
Data:
password: 16 bytes
username: 4 bytes
AppBinding:
Metadata:
Annotations:
kubectl.kubernetes.io/last-applied-configuration: {"apiVersion":"kubedb.com/v1alpha2","kind":"MongoDB","metadata":{"annotations":{},"name":"mgo-replicaset","namespace":"demo"},"spec":{"replicaSet":{"name":"rs0"},"replicas":3,"storage":{"accessModes":["ReadWriteOnce"],"resources":{"requests":{"storage":"1Gi"}},"storageClassName":"standard"},"version":"4.4.26"}}
Creation Timestamp: 2021-02-10T05:07:10Z
Labels:
app.kubernetes.io/component: database
app.kubernetes.io/instance: mgo-replicaset
app.kubernetes.io/managed-by: kubedb.com
app.kubernetes.io/name: mongodbs.kubedb.com
Name: mgo-replicaset
Namespace: demo
Spec:
Client Config:
Service:
Name: mgo-replicaset
Port: 27017
Scheme: mongodb
Parameters:
API Version: config.kubedb.com/v1alpha1
Kind: MongoConfiguration
Replica Sets:
host-0: rs0/mgo-replicaset-0.mgo-replicaset-pods.demo.svc,mgo-replicaset-1.mgo-replicaset-pods.demo.svc,mgo-replicaset-2.mgo-replicaset-pods.demo.svc
Secret:
Name: mgo-replicaset-auth
Type: kubedb.com/mongodb
Version: 4.4.26
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Successful 12m MongoDB operator Successfully created stats service
Normal Successful 12m MongoDB operator Successfully created Service
Normal Successful 12m MongoDB operator Successfully stats service
Normal Successful 12m MongoDB operator Successfully stats service
Normal Successful 11m MongoDB operator Successfully stats service
Normal Successful 11m MongoDB operator Successfully stats service
Normal Successful 11m MongoDB operator Successfully stats service
Normal Successful 11m MongoDB operator Successfully stats service
Normal Successful 10m MongoDB operator Successfully stats service
Normal Successful 10m MongoDB operator Successfully stats service
Normal Successful 10m MongoDB operator Successfully stats service
Normal Successful 10m MongoDB operator Successfully stats service
Normal Successful 10m MongoDB operator Successfully stats service
Normal Successful 10m MongoDB operator Successfully patched StatefulSet demo/mgo-replicaset
Normal Successful 10m MongoDB operator Successfully patched MongoDB
Normal Successful 10m MongoDB operator Successfully created appbinding
Normal Successful 10m MongoDB operator Successfully stats service
Normal Successful 10m MongoDB operator Successfully patched StatefulSet demo/mgo-replicaset
Normal Successful 10m MongoDB operator Successfully patched MongoDB
$ kubectl get statefulset -n demo
NAME READY AGE
mgo-replicaset 3/3 105s
$ kubectl get pvc -n demo
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
datadir-mgo-replicaset-0 Bound pvc-597784c9-c093-11e8-b4a9-0800272618ed 1Gi RWO standard 1h
datadir-mgo-replicaset-1 Bound pvc-8ca7a9d9-c093-11e8-b4a9-0800272618ed 1Gi RWO standard 1h
datadir-mgo-replicaset-2 Bound pvc-b7d8a624-c093-11e8-b4a9-0800272618ed 1Gi RWO standard 1h
$ kubectl get pv -n demo
NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE
pvc-597784c9-c093-11e8-b4a9-0800272618ed 1Gi RWO Delete Bound demo/datadir-mgo-replicaset-0 standard 1h
pvc-8ca7a9d9-c093-11e8-b4a9-0800272618ed 1Gi RWO Delete Bound demo/datadir-mgo-replicaset-1 standard 1h
pvc-b7d8a624-c093-11e8-b4a9-0800272618ed 1Gi RWO Delete Bound demo/datadir-mgo-replicaset-2 standard 1h
$ kubectl get service -n demo
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
mgo-replicaset ClusterIP 10.97.174.220 <none> 27017/TCP 119s
mgo-replicaset-pods ClusterIP None <none> 27017/TCP 119s
KubeDB operator sets the status.phase to Ready once the database is successfully created. Run the following command to see the modified MongoDB object:
$ kubectl get mg -n demo mgo-replicaset -o yaml
apiVersion: kubedb.com/v1alpha2
kind: MongoDB
metadata:
annotations:
kubectl.kubernetes.io/last-applied-configuration: |
{"apiVersion":"kubedb.com/v1alpha2","kind":"MongoDB","metadata":{"annotations":{},"name":"mgo-replicaset","namespace":"demo"},"spec":{"replicaSet":{"name":"rs0"},"replicas":3,"storage":{"accessModes":["ReadWriteOnce"],"resources":{"requests":{"storage":"1Gi"}},"storageClassName":"standard"},"version":"4.4.26"}}
creationTimestamp: "2021-02-11T04:29:29Z"
finalizers:
- kubedb.com
generation: 3
managedFields:
- apiVersion: kubedb.com/v1alpha2
fieldsType: FieldsV1
fieldsV1:
f:metadata:
f:annotations:
.: {}
f:kubectl.kubernetes.io/last-applied-configuration: {}
f:spec:
.: {}
f:replicaSet:
.: {}
f:name: {}
f:replicas: {}
f:storage:
.: {}
f:accessModes: {}
f:resources:
.: {}
f:requests:
.: {}
f:storage: {}
f:storageClassName: {}
f:version: {}
manager: kubectl-client-side-apply
operation: Update
time: "2021-02-11T04:29:29Z"
- apiVersion: kubedb.com/v1alpha2
fieldsType: FieldsV1
fieldsV1:
f:metadata:
f:finalizers: {}
f:spec:
f:authSecret:
.: {}
f:name: {}
f:keyFileSecret:
.: {}
f:name: {}
f:status:
.: {}
f:conditions: {}
f:observedGeneration: {}
f:phase: {}
manager: mg-operator
operation: Update
time: "2021-02-11T04:29:29Z"
name: mgo-replicaset
namespace: demo
resourceVersion: "191685"
uid: 1cc92de5-441e-42ac-8321-459d7a955af2
spec:
authSecret:
name: mgo-replicaset-auth
clusterAuthMode: keyFile
keyFileSecret:
name: mgo-replicaset-key
podTemplate:
controller: {}
metadata: {}
spec:
affinity:
podAntiAffinity:
preferredDuringSchedulingIgnoredDuringExecution:
- podAffinityTerm:
labelSelector:
matchLabels:
app.kubernetes.io/instance: mgo-replicaset
app.kubernetes.io/managed-by: kubedb.com
app.kubernetes.io/name: mongodbs.kubedb.com
namespaces:
- demo
topologyKey: kubernetes.io/hostname
weight: 100
- podAffinityTerm:
labelSelector:
matchLabels:
app.kubernetes.io/instance: mgo-replicaset
app.kubernetes.io/managed-by: kubedb.com
app.kubernetes.io/name: mongodbs.kubedb.com
namespaces:
- demo
topologyKey: failure-domain.beta.kubernetes.io/zone
weight: 50
livenessProbe:
exec:
command:
- bash
- -c
- "set -x; if [[ $(mongo admin --host=localhost --username=$MONGO_INITDB_ROOT_USERNAME
--password=$MONGO_INITDB_ROOT_PASSWORD --authenticationDatabase=admin
--quiet --eval \"db.adminCommand('ping').ok\" ) -eq \"1\" ]]; then \n
\ exit 0\n fi\n exit 1"
failureThreshold: 3
periodSeconds: 10
successThreshold: 1
timeoutSeconds: 5
readinessProbe:
exec:
command:
- bash
- -c
- "set -x; if [[ $(mongo admin --host=localhost --username=$MONGO_INITDB_ROOT_USERNAME
--password=$MONGO_INITDB_ROOT_PASSWORD --authenticationDatabase=admin
--quiet --eval \"db.adminCommand('ping').ok\" ) -eq \"1\" ]]; then \n
\ exit 0\n fi\n exit 1"
failureThreshold: 3
periodSeconds: 10
successThreshold: 1
timeoutSeconds: 1
resources:
limits:
cpu: 500m
memory: 1Gi
requests:
cpu: 500m
memory: 1Gi
serviceAccountName: mgo-replicaset
replicaSet:
name: rs0
replicas: 3
sslMode: disabled
storage:
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 1Gi
storageClassName: standard
storageEngine: wiredTiger
storageType: Durable
terminationPolicy: Delete
version: 4.4.26
status:
conditions:
- lastTransitionTime: "2021-02-11T04:29:29Z"
message: 'The KubeDB operator has started the provisioning of MongoDB: demo/mgo-replicaset'
reason: DatabaseProvisioningStartedSuccessfully
status: "True"
type: ProvisioningStarted
- lastTransitionTime: "2021-02-11T04:31:22Z"
message: All desired replicas are ready.
reason: AllReplicasReady
status: "True"
type: ReplicaReady
- lastTransitionTime: "2021-02-11T04:31:11Z"
message: 'The MongoDB: demo/mgo-replicaset is accepting client requests.'
observedGeneration: 3
reason: DatabaseAcceptingConnectionRequest
status: "True"
type: AcceptingConnection
- lastTransitionTime: "2021-02-11T04:31:11Z"
message: 'The MongoDB: demo/mgo-replicaset is ready.'
observedGeneration: 3
reason: ReadinessCheckSucceeded
status: "True"
type: Ready
- lastTransitionTime: "2021-02-11T04:31:22Z"
message: 'The MongoDB: demo/mgo-replicaset is successfully provisioned.'
observedGeneration: 3
reason: DatabaseSuccessfullyProvisioned
status: "True"
type: Provisioned
observedGeneration: 3
phase: Ready
Please note that KubeDB operator has created a new Secret called mgo-replicaset-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.authSecret.name. While creating this secret manually, make sure the secret contains these two keys containing data username and password. For more details, please see here.
Redundancy and Data Availability
Now, you can connect to this database through mgo-replicaset. In this tutorial, we will insert document on the primary member, and we will see if the data becomes available on secondary members.
At first, insert data inside primary member rs0:PRIMARY.
$ kubectl get secrets -n demo mgo-replicaset-auth -o jsonpath='{.data.\username}' | base64 -d
root
$ kubectl get secrets -n demo mgo-replicaset-auth -o jsonpath='{.data.\password}' | base64 -d
5O4R2ze2bWXcWsdP
$ kubectl exec -it mgo-replicaset-0 -n demo bash
mongodb@mgo-replicaset-0:/$ mongo admin -u root -p 5O4R2ze2bWXcWsdP
MongoDB shell version v4.4.26
connecting to: mongodb://127.0.0.1:27017/admin
MongoDB server version: 4.4.26
Welcome to the MongoDB shell.
rs0:PRIMARY> > rs.isMaster().primary
mgo-replicaset-0.mgo-replicaset-gvr.demo.svc.cluster.local:27017
rs0:PRIMARY> show dbs
admin 0.000GB
config 0.000GB
local 0.000GB
rs0:PRIMARY> show users
{
"_id" : "admin.root",
"userId" : UUID("6b714456-2914-4ea0-9596-92249e8285a2"),
"user" : "root",
"db" : "admin",
"roles" : [
{
"role" : "root",
"db" : "admin"
}
],
"mechanisms" : [
"SCRAM-SHA-1",
"SCRAM-SHA-256"
]
}
rs0:PRIMARY> use newdb
switched to db newdb
rs0:PRIMARY> db.movie.insert({"name":"batman"});
WriteResult({ "nInserted" : 1 })
rs0:PRIMARY> db.movie.find().pretty()
{ "_id" : ObjectId("5b5efeea9d097ca0600694a3"), "name" : "batman" }
rs0:PRIMARY> exit
bye
Now, check the redundancy and data availability in secondary members.
We will exec in mgo-replicaset-1(which is secondary member right now) to check the data availability.
$ kubectl exec -it mgo-replicaset-1 -n demo bash
mongodb@mgo-replicaset-1:/$ mongo admin -u root -p 5O4R2ze2bWXcWsdP
MongoDB shell version v4.4.26
connecting to: mongodb://127.0.0.1:27017/admin
MongoDB server version: 4.4.26
Welcome to the MongoDB shell.
rs0:SECONDARY> rs.slaveOk()
rs0:SECONDARY> > show dbs
admin 0.000GB
config 0.000GB
local 0.000GB
newdb 0.000GB
rs0:SECONDARY> show users
{
"_id" : "admin.root",
"userId" : UUID("6b714456-2914-4ea0-9596-92249e8285a2"),
"user" : "root",
"db" : "admin",
"roles" : [
{
"role" : "root",
"db" : "admin"
}
],
"mechanisms" : [
"SCRAM-SHA-1",
"SCRAM-SHA-256"
]
}
rs0:SECONDARY> use newdb
switched to db newdb
rs0:SECONDARY> db.movie.find().pretty()
{ "_id" : ObjectId("5b5efeea9d097ca0600694a3"), "name" : "batman" }
rs0:SECONDARY> exit
bye
Automatic Failover
To test automatic failover, we will force the primary member to restart. As the primary member (pod) becomes unavailable, the rest of the members will elect a primary member by election.
$ kubectl get pods -n demo
NAME READY STATUS RESTARTS AGE
mgo-replicaset-0 1/1 Running 0 1h
mgo-replicaset-1 1/1 Running 0 1h
mgo-replicaset-2 1/1 Running 0 1h
$ kubectl delete pod -n demo mgo-replicaset-0
pod "mgo-replicaset-0" deleted
$ kubectl get pods -n demo
NAME READY STATUS RESTARTS AGE
mgo-replicaset-0 1/1 Terminating 0 1h
mgo-replicaset-1 1/1 Running 0 1h
mgo-replicaset-2 1/1 Running 0 1h
Now verify the automatic failover, Let’s exec in mgo-replicaset-1 pod,
$ kubectl exec -it mgo-replicaset-1 -n demo bash
mongodb@mgo-replicaset-1:/$ mongo admin -u root -p 5O4R2ze2bWXcWsdP
MongoDB shell version v4.4.26
connecting to: mongodb://127.0.0.1:27017/admin
MongoDB server version: 4.4.26
Welcome to the MongoDB shell.
rs0:SECONDARY> rs.isMaster().primary
mgo-replicaset-2.mgo-replicaset-gvr.demo.svc.cluster.local:27017
# Also verify, data persistency
rs0:SECONDARY> rs.slaveOk()
rs0:SECONDARY> > show dbs
admin 0.000GB
config 0.000GB
local 0.000GB
newdb 0.000GB
rs0:SECONDARY> show users
{
"_id" : "admin.root",
"userId" : UUID("6b714456-2914-4ea0-9596-92249e8285a2"),
"user" : "root",
"db" : "admin",
"roles" : [
{
"role" : "root",
"db" : "admin"
}
],
"mechanisms" : [
"SCRAM-SHA-1",
"SCRAM-SHA-256"
]
}
rs0:SECONDARY> use newdb
switched to db newdb
rs0:SECONDARY> db.movie.find().pretty()
{ "_id" : ObjectId("5b5efeea9d097ca0600694a3"), "name" : "batman" }
Halt Database
When TerminationPolicy is set to halt, and you delete the mongodb object, the KubeDB operator will delete the StatefulSet and its pods but leaves the PVCs, secrets and database backup (snapshots) intact. Learn details of all TerminationPolicy here.
You can also keep the mongodb object and halt the database to resume it again later. If you halt the database, the kubedb will delete the statefulsets and services but will keep the mongodb object, pvcs, secrets and backup (snapshots).
To halt the database, first you have to set the terminationPolicy to Halt in existing database. You can use the below command to set the terminationPolicy to Halt, if it is not already set.
$ kubectl patch -n demo mg/mgo-replicaset -p '{"spec":{"terminationPolicy":"Halt"}}' --type="merge"
mongodb.kubedb.com/mgo-replicaset patched
Then, you have to set the spec.halted as true to set the database in a Halted state. You can use the below command.
$ kubectl patch -n demo mg/mgo-replicaset -p '{"spec":{"halted":true}}' --type="merge"
mongodb.kubedb.com/mgo-replicaset patched
After that, kubedb will delete the statefulsets and services and you can see the database Phase as Halted.
Now, you can run the following command to get all mongodb resources in demo namespaces,
$ kubectl get mg,sts,svc,secret,pvc -n demo
NAME VERSION STATUS AGE
mongodb.kubedb.com/mgo-replicaset 4.4.26 Halted 9m43s
NAME TYPE DATA AGE
secret/default-token-x2zcl kubernetes.io/service-account-token 3 47h
secret/mgo-replicaset-auth Opaque 2 23h
secret/mgo-replicaset-key Opaque 1 23h
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
persistentvolumeclaim/datadir-mgo-replicaset-0 Bound pvc-816daa52-ee40-496f-a148-c75344a1b433 1Gi RWO standard 9m43s
persistentvolumeclaim/datadir-mgo-replicaset-1 Bound pvc-e818bc86-ab3c-4ec5-901f-630aab6b814b 1Gi RWO standard 9m5s
persistentvolumeclaim/datadir-mgo-replicaset-2 Bound pvc-5a50bce3-f85f-4157-be22-64dfc26e7517 1Gi RWO standard 8m25s
Resume Halted Database
Now, to resume the database, i.e. to get the same database setup back again, you have to set the the spec.halted as false. You can use the below command.
$ kubectl patch -n demo mg/mgo-replicaset -p '{"spec":{"halted":false}}' --type="merge"
mongodb.kubedb.com/mgo-replicaset patched
When the database is resumed successfully, you can see the database Status is set to Ready.
$ kubectl get mg -n demo
NAME VERSION STATUS AGE
mgo-replicaset 4.4.26 Ready 6m27s
Now, If you again exec into the primary pod and look for previous data, you will see that, all the data persists.
$ kubectl exec -it mgo-replicaset-1 -n demo bash
mongodb@mgo-replicaset-1:/$ mongo admin -u root -p 7QiqLcuSCmZ8PU5a
rs0:PRIMARY> use newdb
switched to db newdb
rs0:PRIMARY> db.movie.find()
{ "_id" : ObjectId("6024b3e47c614cd582c9bb44"), "name" : "batman" }
Cleaning up
To cleanup the Kubernetes resources created by this tutorial, run:
kubectl patch -n demo mg/mgo-replicaset -p '{"spec":{"terminationPolicy":"WipeOut"}}' --type="merge"
kubectl delete -n demo mg/mgo-replicaset
kubectl delete ns demo
Next Steps
- Backup and Restore process of MongoDB databases using Stash.
- Initialize MongoDB with Script.
- Monitor your MongoDB database with KubeDB using out-of-the-box 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.