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KubeDB - MongoDB ReplicaSet with Arbiter
This tutorial will show you how to use KubeDB to run a MongoDB ReplicaSet with arbiter.
Before You Begin
Before proceeding:
Read mongodb arbiter concept to get the concept about MongoDB Replica Set Arbiter.
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 with arbiter
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: mongo-arb
namespace: demo
spec:
version: "4.4.26"
replicaSet:
name: "rs0"
replicas: 2
storageType: Durable
storage:
storageClassName: "standard"
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 500Mi
arbiter:
podTemplate: {}
terminationPolicy: WipeOut
$ kubectl create -f https://github.com/kubedb/docs/raw/v2024.7.3-rc.0/docs/examples/mongodb/arbiter/replicaset.yaml
mongodb.kubedb.com/mongo-arb 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 data-bearing 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.spec.arbiterdenotes arbiter spec of the deployed MongoDB CRD. There are two fields under it : configSecret & podTemplate.spec.arbiter.configSecretis an optional field to provide custom configuration file for database (i.e mongod.cnf). If specified, this file will be used as configuration file otherwise default configuration file will be used.spec.arbiter.podTemplateholds the arbiter-podSpec.nullvalue of it, instructs kubedb operator to use the default arbiter podTemplate.
KubeDB operator watches for MongoDB objects using Kubernetes api. When a MongoDB object is created, KubeDB operator will create two new StatefulSets (one for replicas & one for arbiter) 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 the pods of those two StatefulSets with the name <mongodb-name>-pods.
$ kubectl dba describe mg -n demo mongo-arb
Name: mongo-arb
Namespace: demo
CreationTimestamp: Thu, 21 Apr 2022 14:39:32 +0600
Labels: <none>
Annotations: kubectl.kubernetes.io/last-applied-configuration={"apiVersion":"kubedb.com/v1alpha2","kind":"MongoDB","metadata":{"annotations":{},"name":"mongo-arb","namespace":"demo"},"spec":{"arbiter":{"podTemplat...
Replicas: 2 total
Status: Ready
StorageType: Durable
Volume:
StorageClass: standard
Capacity: 500Mi
Access Modes: RWO
Paused: false
Halted: false
Termination Policy: WipeOut
StatefulSet:
Name: mongo-arb
CreationTimestamp: Thu, 21 Apr 2022 14:39:32 +0600
Labels: app.kubernetes.io/component=database
app.kubernetes.io/instance=mongo-arb
app.kubernetes.io/managed-by=kubedb.com
app.kubernetes.io/name=mongodbs.kubedb.com
mongodb.kubedb.com/node.type=replica
Annotations: <none>
Replicas: 824639168104 desired | 2 total
Pods Status: 2 Running / 0 Waiting / 0 Succeeded / 0 Failed
StatefulSet:
Name: mongo-arb-arbiter
CreationTimestamp: Thu, 21 Apr 2022 14:40:21 +0600
Labels: app.kubernetes.io/component=database
app.kubernetes.io/instance=mongo-arb
app.kubernetes.io/managed-by=kubedb.com
app.kubernetes.io/name=mongodbs.kubedb.com
mongodb.kubedb.com/node.type=arbiter
Annotations: <none>
Replicas: 824645537528 desired | 1 total
Pods Status: 1 Running / 0 Waiting / 0 Succeeded / 0 Failed
Service:
Name: mongo-arb
Labels: app.kubernetes.io/component=database
app.kubernetes.io/instance=mongo-arb
app.kubernetes.io/managed-by=kubedb.com
app.kubernetes.io/name=mongodbs.kubedb.com
Annotations: <none>
Type: ClusterIP
IP: 10.96.148.184
Port: primary 27017/TCP
TargetPort: db/TCP
Endpoints: 10.244.3.23:27017
Service:
Name: mongo-arb-pods
Labels: app.kubernetes.io/component=database
app.kubernetes.io/instance=mongo-arb
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: 10.244.1.9:27017,10.244.2.18:27017,10.244.3.23:27017
Auth Secret:
Name: mongo-arb-auth
Labels: app.kubernetes.io/component=database
app.kubernetes.io/instance=mongo-arb
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":"mongo-arb","namespace":"demo"},"spec":{"arbiter":{"podTemplate":null},"replicaSet":{"name":"rs0"},"replicas":2,"storage":{"accessModes":["ReadWriteOnce"],"resources":{"requests":{"storage":"500Mi"}},"storageClassName":"standard"},"storageType":"Durable","terminationPolicy":"WipeOut","version":"4.4.26"}}
Creation Timestamp: 2022-04-21T08:40:21Z
Labels:
app.kubernetes.io/component: database
app.kubernetes.io/instance: mongo-arb
app.kubernetes.io/managed-by: kubedb.com
app.kubernetes.io/name: mongodbs.kubedb.com
Name: mongo-arb
Namespace: demo
Spec:
Client Config:
Service:
Name: mongo-arb
Port: 27017
Scheme: mongodb
Parameters:
API Version: config.kubedb.com/v1alpha1
Kind: MongoConfiguration
Replica Sets:
host-0: rs0/mongo-arb-0.mongo-arb-pods.demo.svc:27017,mongo-arb-1.mongo-arb-pods.demo.svc:27017,mongo-arb-arbiter-0.mongo-arb-pods.demo.svc:27017
Stash:
Addon:
Backup Task:
Name: mongodb-backup-4.4.6
Restore Task:
Name: mongodb-restore-4.4.6
Secret:
Name: mongo-arb-auth
Type: kubedb.com/mongodb
Version: 4.4.26
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Successful 1m Postgres operator Successfully created governing service
Normal Successful 1m Postgres operator Successfully created Primary Service
Normal Successful 1m Postgres operator Successfully created appbinding
$ kubectl get statefulset -n demo
NAME READY AGE
mongo-arb 2/2 2m37s
mongo-arb-arbiter 1/1 108s
$ kubectl get pvc -n demo
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
datadir-mongo-arb-0 Bound pvc-93a2681f-096d-4af1-b1fb-93cd7b7b6020 500Mi RWO standard 2m57s
datadir-mongo-arb-1 Bound pvc-fb06ea3b-a9dd-4479-87b2-de73ca272718 500Mi RWO standard 2m35s
datadir-mongo-arb-arbiter-0 Bound pvc-169fd172-0e41-48e3-81a5-3abae4a85056 500Mi RWO standard 2m8s
$ kubectl get pv -n demo
NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE
pvc-169fd172-0e41-48e3-81a5-3abae4a85056 500Mi RWO Delete Bound demo/datadir-mongo-arb-arbiter-0 standard 2m23s
pvc-93a2681f-096d-4af1-b1fb-93cd7b7b6020 500Mi RWO Delete Bound demo/datadir-mongo-arb-0 standard 3m11s
pvc-fb06ea3b-a9dd-4479-87b2-de73ca272718 500Mi RWO Delete Bound demo/datadir-mongo-arb-1 standard 2m50s
$ kubectl get service -n demo
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
mongo-arb ClusterIP 10.96.148.184 <none> 27017/TCP 3m32s
mongo-arb-pods ClusterIP None <none> 27017/TCP 3m32s
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 mongo-arb -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":"mongo-arb","namespace":"demo"},"spec":{"arbiter":{"podTemplate":null},"replicaSet":{"name":"rs0"},"replicas":2,"storage":{"accessModes":["ReadWriteOnce"],"resources":{"requests":{"storage":"500Mi"}},"storageClassName":"standard"},"storageType":"Durable","terminationPolicy":"WipeOut","version":"4.4.26"}}
creationTimestamp: "2022-04-21T08:39:32Z"
finalizers:
- kubedb.com
generation: 3
name: mongo-arb
namespace: demo
resourceVersion: "22168"
uid: c4a3dc69-5556-42b6-a2b8-11d3547015d3
spec:
allowedSchemas:
namespaces:
from: Same
arbiter:
podTemplate:
controller: {}
metadata: {}
spec:
affinity:
podAntiAffinity:
preferredDuringSchedulingIgnoredDuringExecution:
- podAffinityTerm:
labelSelector:
matchLabels:
app.kubernetes.io/instance: mongo-arb
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: mongo-arb
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 --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 --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:
memory: 1Gi
requests:
cpu: 500m
memory: 1Gi
authSecret:
name: mongo-arb-auth
clusterAuthMode: keyFile
coordinator:
resources: {}
keyFileSecret:
name: mongo-arb-key
podTemplate:
controller: {}
metadata: {}
spec:
affinity:
podAntiAffinity:
preferredDuringSchedulingIgnoredDuringExecution:
- podAffinityTerm:
labelSelector:
matchLabels:
app.kubernetes.io/instance: mongo-arb
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: mongo-arb
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:
memory: 1Gi
requests:
cpu: 500m
memory: 1Gi
serviceAccountName: mongo-arb
replicaSet:
name: rs0
replicas: 2
sslMode: disabled
storage:
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 500Mi
storageClassName: standard
storageEngine: wiredTiger
storageType: Durable
terminationPolicy: WipeOut
version: 4.4.26
status:
conditions:
- lastTransitionTime: "2022-04-21T08:39:32Z"
message: 'The KubeDB operator has started the provisioning of MongoDB: demo/mongo-arb'
reason: DatabaseProvisioningStartedSuccessfully
status: "True"
type: ProvisioningStarted
- lastTransitionTime: "2022-04-21T08:40:42Z"
message: All desired replicas are ready.
reason: AllReplicasReady
status: "True"
type: ReplicaReady
- lastTransitionTime: "2022-04-21T08:39:56Z"
message: 'The MongoDB: demo/mongo-arb is accepting client requests.'
observedGeneration: 3
reason: DatabaseAcceptingConnectionRequest
status: "True"
type: AcceptingConnection
- lastTransitionTime: "2022-04-21T08:39:56Z"
message: 'The MongoDB: demo/mongo-arb is ready.'
observedGeneration: 3
reason: ReadinessCheckSucceeded
status: "True"
type: Ready
- lastTransitionTime: "2022-04-21T08:40:21Z"
message: 'The MongoDB: demo/mongo-arb 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 mongo-arb-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 mongo-arb. 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 mongo-arb-auth -o jsonpath='{.data.\username}' | base64 -d
root
$ kubectl get secrets -n demo mongo-arb-auth -o jsonpath='{.data.\password}' | base64 -d
OX4yb!IFm;~yAHkD
$ kubectl exec -it mongo-arb-0 -n demo bash
mongodb@mongo-arb-0:/$ mongo admin -u root -p 'OX4yb!IFm;~yAHkD'
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.status()
{
"set" : "rs0",
"date" : ISODate("2022-04-21T08:46:28.786Z"),
"myState" : 1,
"term" : NumberLong(1),
"syncSourceHost" : "",
"syncSourceId" : -1,
"heartbeatIntervalMillis" : NumberLong(2000),
"majorityVoteCount" : 2,
"writeMajorityCount" : 2,
"votingMembersCount" : 3,
"writableVotingMembersCount" : 2,
"optimes" : {
"lastCommittedOpTime" : {
"ts" : Timestamp(1650530787, 1),
"t" : NumberLong(1)
},
"lastCommittedWallTime" : ISODate("2022-04-21T08:46:27.247Z"),
"readConcernMajorityOpTime" : {
"ts" : Timestamp(1650530787, 1),
"t" : NumberLong(1)
},
"readConcernMajorityWallTime" : ISODate("2022-04-21T08:46:27.247Z"),
"appliedOpTime" : {
"ts" : Timestamp(1650530787, 1),
"t" : NumberLong(1)
},
"durableOpTime" : {
"ts" : Timestamp(1650530787, 1),
"t" : NumberLong(1)
},
"lastAppliedWallTime" : ISODate("2022-04-21T08:46:27.247Z"),
"lastDurableWallTime" : ISODate("2022-04-21T08:46:27.247Z")
},
"lastStableRecoveryTimestamp" : Timestamp(1650530747, 1),
"electionCandidateMetrics" : {
"lastElectionReason" : "electionTimeout",
"lastElectionDate" : ISODate("2022-04-21T08:39:47.205Z"),
"electionTerm" : NumberLong(1),
"lastCommittedOpTimeAtElection" : {
"ts" : Timestamp(0, 0),
"t" : NumberLong(-1)
},
"lastSeenOpTimeAtElection" : {
"ts" : Timestamp(1650530387, 1),
"t" : NumberLong(-1)
},
"numVotesNeeded" : 1,
"priorityAtElection" : 1,
"electionTimeoutMillis" : NumberLong(10000),
"newTermStartDate" : ISODate("2022-04-21T08:39:47.221Z"),
"wMajorityWriteAvailabilityDate" : ISODate("2022-04-21T08:39:47.234Z")
},
"members" : [
{
"_id" : 0,
"name" : "mongo-arb-0.mongo-arb-pods.demo.svc.cluster.local:27017",
"health" : 1,
"state" : 1,
"stateStr" : "PRIMARY",
"uptime" : 412,
"optime" : {
"ts" : Timestamp(1650530787, 1),
"t" : NumberLong(1)
},
"optimeDate" : ISODate("2022-04-21T08:46:27Z"),
"syncSourceHost" : "",
"syncSourceId" : -1,
"infoMessage" : "",
"electionTime" : Timestamp(1650530387, 2),
"electionDate" : ISODate("2022-04-21T08:39:47Z"),
"configVersion" : 3,
"configTerm" : 1,
"self" : true,
"lastHeartbeatMessage" : ""
},
{
"_id" : 1,
"name" : "mongo-arb-1.mongo-arb-pods.demo.svc.cluster.local:27017",
"health" : 1,
"state" : 2,
"stateStr" : "SECONDARY",
"uptime" : 375,
"optime" : {
"ts" : Timestamp(1650530787, 1),
"t" : NumberLong(1)
},
"optimeDurable" : {
"ts" : Timestamp(1650530787, 1),
"t" : NumberLong(1)
},
"optimeDate" : ISODate("2022-04-21T08:46:27Z"),
"optimeDurableDate" : ISODate("2022-04-21T08:46:27Z"),
"lastHeartbeat" : ISODate("2022-04-21T08:46:27.456Z"),
"lastHeartbeatRecv" : ISODate("2022-04-21T08:46:27.591Z"),
"pingMs" : NumberLong(0),
"lastHeartbeatMessage" : "",
"syncSourceHost" : "mongo-arb-0.mongo-arb-pods.demo.svc.cluster.local:27017",
"syncSourceId" : 0,
"infoMessage" : "",
"configVersion" : 3,
"configTerm" : 1
},
{
"_id" : 2,
"name" : "mongo-arb-arbiter-0.mongo-arb-pods.demo.svc.cluster.local:27017",
"health" : 1,
"state" : 7,
"stateStr" : "ARBITER",
"uptime" : 353,
"lastHeartbeat" : ISODate("2022-04-21T08:46:27.450Z"),
"lastHeartbeatRecv" : ISODate("2022-04-21T08:46:27.607Z"),
"pingMs" : NumberLong(0),
"lastHeartbeatMessage" : "",
"syncSourceHost" : "",
"syncSourceId" : -1,
"infoMessage" : "",
"configVersion" : 3,
"configTerm" : 1
}
],
"ok" : 1,
"$clusterTime" : {
"clusterTime" : Timestamp(1650530787, 1),
"signature" : {
"hash" : BinData(0,"N6pWJaxVqaZch7cKLKWX8bdfkBM="),
"keyId" : NumberLong("7088974033219223556")
}
},
"operationTime" : Timestamp(1650530787, 1)
}
Here you can see the arbiter pod in the members list of rs.status() output.
rs0:PRIMARY> > rs.isMaster().primary
mongo-arb-0.mongo-arb-pods.demo.svc.cluster.local:27017
rs0:PRIMARY> show dbs
admin 0.000GB
config 0.000GB
kubedb-system 0.000GB
local 0.000GB
rs0:PRIMARY> show users
{
"_id" : "admin.root",
"userId" : UUID("af3c1344-d052-496a-bdbb-5bd41486d878"),
"user" : "root",
"db" : "admin",
"roles" : [
{
"role" : "root",
"db" : "admin"
}
],
"mechanisms" : [
"SCRAM-SHA-1",
"SCRAM-SHA-256"
]
}
rs0:PRIMARY> use mydb
switched to db mydb
rs0:PRIMARY> db.songs.insert({"pink floyd": "shine on you crazy diamond"})
WriteResult({ "nInserted" : 1 })
rs0:PRIMARY> db.songs.find().pretty()
{
"_id" : ObjectId("62611ae33583279dfca0a5e4"),
"pink floyd" : "shine on you crazy diamond"
}
rs0:PRIMARY> exit
bye
Now, check the redundancy and data availability in secondary members.
We will exec in mongo-arb-1(which is secondary member right now) to check the data availability.
$ kubectl exec -it mongo-arb-1 -n demo bash
mongodb@mongo-arb-1:/$ mongo admin -u root -p 'OX4yb!IFm;~yAHkD'
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
kubedb-system 0.000GB
local 0.000GB
mydb 0.000GB
rs0:SECONDARY> show users
{
"_id" : "admin.root",
"userId" : UUID("af3c1344-d052-496a-bdbb-5bd41486d878"),
"user" : "root",
"db" : "admin",
"roles" : [
{
"role" : "root",
"db" : "admin"
}
],
"mechanisms" : [
"SCRAM-SHA-1",
"SCRAM-SHA-256"
]
}
rs0:SECONDARY> use mydb
switched to db mydb
rs0:SECONDARY> db.songs.find().pretty()
{
"_id" : ObjectId("62611ae33583279dfca0a5e4"),
"pink floyd" : "shine on you crazy diamond"
}
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
mongo-arb-0 2/2 Running 0 15m
mongo-arb-1 2/2 Running 0 14m
mongo-arb-arbiter-0 1/1 Running 0 14m
$ kubectl delete pod -n demo mongo-arb-0
pod "mongo-arb-0" deleted
$ kubectl get pods -n demo
NAME READY STATUS RESTARTS AGE
mongo-arb-0 2/2 Terminating 0 16m
mongo-arb-1 2/2 Running 0 15m
mongo-arb-arbiter-0 1/1 Running 0 15m
Now verify the automatic failover, Let’s exec in mongo-arb-0 pod,
$ kubectl exec -it mongo-arb-0 -n demo bash
mongodb@mongo-arb-1:/$ mongo admin -u root -p 'OX4yb!IFm;~yAHkD'
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
mongo-arb-1.mongo-arb-pods.demo.svc.cluster.local:27017
# Also verify, data persistency
rs0:SECONDARY> rs.slaveOk()
rs0:SECONDARY> > show dbs
admin 0.000GB
config 0.000GB
kubedb-system 0.000GB
local 0.000GB
mydb 0.000GB
rs0:SECONDARY> use mydb
switched to db mydb
rs0:SECONDARY> db.songs.find().pretty()
{
"_id" : ObjectId("62611ae33583279dfca0a5e4"),
"pink floyd" : "shine on you crazy diamond"
}
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/mongo-arb -p '{"spec":{"terminationPolicy":"Halt"}}' --type="merge"
mongodb.kubedb.com/mongo-arb 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/mongo-arb -p '{"spec":{"halted":true}}' --type="merge"
mongodb.kubedb.com/mongo-arb 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/mongo-arb 4.4.26 Halted 21m
NAME TYPE DATA AGE
secret/default-token-nzk64 kubernetes.io/service-account-token 3 146m
secret/mongo-arb-auth Opaque 2 21m
secret/mongo-arb-key Opaque 1 21m
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
persistentvolumeclaim/datadir-mongo-arb-0 Bound pvc-93a2681f-096d-4af1-b1fb-93cd7b7b6020 500Mi RWO standard 21m
persistentvolumeclaim/datadir-mongo-arb-1 Bound pvc-fb06ea3b-a9dd-4479-87b2-de73ca272718 500Mi RWO standard 21m
persistentvolumeclaim/datadir-mongo-arb-arbiter-0 Bound pvc-169fd172-0e41-48e3-81a5-3abae4a85056 500Mi RWO standard 21m
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/mongo-arb -p '{"spec":{"halted":false}}' --type="merge"
mongodb.kubedb.com/mongo-arb 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
mongodb.kubedb.com/mongo-arb 4.4.26 Ready 23m
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 mongo-arb-1 -n demo bash
mongodb@mongo-arb-1:/$ mongo admin -u root -p 'OX4yb!IFm;~yAHkD'
rs0:PRIMARY> use mydb
switched to db mydb
rs0:PRIMARY> db.songs.find().pretty()
{
"_id" : ObjectId("62611ae33583279dfca0a5e4"),
"pink floyd" : "shine on you crazy diamond"
}
Cleaning up
To cleanup the Kubernetes resources created by this tutorial, run:
kubectl patch -n demo mg/mongo-arb -p '{"spec":{"terminationPolicy":"WipeOut"}}' --type="merge"
kubectl delete -n demo mg/mongo-arb
kubectl delete ns demo
Next Steps
- Deploy MongoDB shard with Arbiter.
- 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.