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KubeDB - MySQL Group Replication
This tutorial will show you how to use KubeDB to provision a MySQL replication group in single-primary mode.
Before You Begin
Before proceeding:
Read mysql group replication concept to learn about MySQL Group Replication.
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/guides/mysql/clustering/group-replication/yamls folder in GitHub repository kubedb/docs.
Deploy MySQL Cluster
To deploy a single primary MySQL replication group , specify spec.topology field in MySQL CRD.
The following is an example MySQL object which creates a MySQL group with three members (one is primary member and the two others are secondary members).
apiVersion: kubedb.com/v1alpha2
kind: MySQL
metadata:
name: my-group
namespace: demo
spec:
version: "8.0.23-v1"
replicas: 3
topology:
mode: GroupReplication
group:
name: "dc002fc3-c412-4d18-b1d4-66c1fbfbbc9b"
storageType: Durable
storage:
storageClassName: "standard"
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 1Gi
terminationPolicy: WipeOut
$ kubectl create -f https://github.com/kubedb/docs/raw/v2021.06.23/docs/guides/mysql/clustering/group-replication/yamls/group-replication.yaml
mysql.kubedb.com/my-group created
Here,
spec.topologytells about the clustering configuration for MySQL.spec.topology.modespecifies the mode for MySQL cluster. Here we have usedGroupReplicationto tell the operator that we want to deploy a MySQL replication group.spec.topology.groupcontains group replication info.spec.topology.group.namethe name for the group. It is a valid version 4 UUID.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 MySQL objects using Kubernetes API. When a MySQL object is created, KubeDB operator will create a new StatefulSet and a Service with the matching MySQL object name. KubeDB operator will also create a governing service for the StatefulSet with the name <mysql-object-name>-pods.
$ kubectl dba describe my -n demo my-group
Name: my-group
Namespace: demo
CreationTimestamp: Tue, 25 Aug 2020 16:42:10 +0600
Labels: <none>
Annotations: kubectl.kubernetes.io/last-applied-configuration={"apiVersion":"kubedb.com/v1alpha2","kind":"MySQL","metadata":{"annotations":{},"name":"my-group","namespace":"demo"},"spec":{"replicas":3,"storage":{"...
Replicas: 3 total
Status: Running
StorageType: Durable
Volume:
StorageClass: standard
Capacity: 1Gi
Access Modes: RWO
Halted: false
Halted: false
Termination Policy: WipeOut
StatefulSet:
Name: my-group
CreationTimestamp: Tue, 25 Aug 2020 16:42:10 +0600
Labels: app.kubernetes.io/component=database
app.kubernetes.io/managed-by=kubedb.com
app.kubernetes.io/name=mysqls.kubedb.com
app.kubernetes.io/instance=my-group
Annotations: <none>
Replicas: 824638237768 desired | 3 total
Pods Status: 3 Running / 0 Waiting / 0 Succeeded / 0 Failed
Service:
Name: my-group
Labels: app.kubernetes.io/component=database
app.kubernetes.io/managed-by=kubedb.com
app.kubernetes.io/name=mysqls.kubedb.com
app.kubernetes.io/instance=my-group
Annotations: <none>
Type: ClusterIP
IP: 10.109.225.127
Port: db 3306/TCP
TargetPort: db/TCP
Endpoints: 10.244.1.4:3306,10.244.1.6:3306,10.244.2.4:3306
Service:
Name: my-group-pods
Labels: app.kubernetes.io/component=database
app.kubernetes.io/managed-by=kubedb.com
app.kubernetes.io/name=mysqls.kubedb.com
app.kubernetes.io/instance=my-group
Annotations: service.alpha.kubernetes.io/tolerate-unready-endpoints=true
Type: ClusterIP
IP: None
Port: db 3306/TCP
TargetPort: 3306/TCP
Endpoints: 10.244.1.4:3306,10.244.1.6:3306,10.244.2.4:3306
Service:
Name: my-group-primary
Labels: app.kubernetes.io/component=database
app.kubernetes.io/managed-by=kubedb.com
app.kubernetes.io/name=mysqls.kubedb.com
app.kubernetes.io/instance=my-group
Annotations: <none>
Type: ClusterIP
IP: 10.111.57.60
Port: db 3306/TCP
TargetPort: db/TCP
Endpoints: 10.244.2.4:3306
Database Secret:
Name: my-group-auth
Labels: app.kubernetes.io/component=database
app.kubernetes.io/managed-by=kubedb.com
app.kubernetes.io/name=mysqls.kubedb.com
app.kubernetes.io/instance=my-group
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":"MySQL","metadata":{"annotations":{},"name":"my-group","namespace":"demo"},"spec":{"replicas":3,"storage":{"accessModes":["ReadWriteOnce"],"resources":{"requests":{"storage":"1Gi"}},"storageClassName":"standard"},"storageType":"Durable","terminationPolicy":"WipeOut","topology":{"group":{"baseServerID":100,"name":"dc002fc3-c412-4d18-b1d4-66c1fbfbbc9b"},"mode":"GroupReplication"},"version":"8.0.23-v1"}}
Creation Timestamp: 2020-08-25T10:50:59Z
Labels:
app.kubernetes.io/component: database
app.kubernetes.io/instance: my-group
app.kubernetes.io/managed-by: kubedb.com
app.kubernetes.io/name: mysql
app.kubernetes.io/version: 8.0.23-v1
app.kubernetes.io/name: mysqls.kubedb.com
app.kubernetes.io/instance: my-group
Name: my-group
Namespace: demo
Spec:
Client Config:
Service:
Name: my-group
Path: /
Port: 3306
Scheme: mysql
URL: tcp(my-group:3306)/
Secret:
Name: my-group-auth
Type: kubedb.com/mysql
Version: 8.0.23-v1
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Successful 12m MySQL operator Successfully created Service
Normal Successful 12m MySQL operator Successfully created primary service
Normal Successful 4m MySQL operator Successfully created StatefulSet
Normal Successful 4m MySQL operator Successfully created MySQL
Normal Successful 4m MySQL operator Successfully created appbinding
$ kubectl get statefulset -n demo
NAME READY AGE
my-group 3/3 49m
$ kubectl get pvc -n demo
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
data-my-group-0 Bound pvc-ea20656d-6809-11e9-89c6-080027fc7fb2 1Gi RWO standard 49m
data-my-group-1 Bound pvc-4a2d43b0-680a-11e9-89c6-080027fc7fb2 1Gi RWO standard 47m
data-my-group-2 Bound pvc-60558ef0-680a-11e9-89c6-080027fc7fb2 1Gi RWO standard 46m
$ kubectl get pv -n demo
NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE
pvc-4a2d43b0-680a-11e9-89c6-080027fc7fb2 1Gi RWO Delete Bound demo/data-my-group-1 standard 56m
pvc-60558ef0-680a-11e9-89c6-080027fc7fb2 1Gi RWO Delete Bound demo/data-my-group-2 standard 55m
pvc-ea20656d-6809-11e9-89c6-080027fc7fb2 1Gi RWO Delete Bound demo/data-my-group-0 standard 59m
$ kubectl get service -n demo
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
my-group ClusterIP 10.109.225.127 <none> 3306/TCP 17m
my-group-pods ClusterIP None <none> 3306/TCP 17m
my-group-primary ClusterIP 10.111.57.60 <none> 3306/TCP 17m
KubeDB operator sets the status.phase to Running once the database is successfully created. Run the following command to see the modified MySQL object:
$ kubectl get my -n demo my-group -o yaml | kubectl neat
apiVersion: kubedb.com/v1alpha2
kind: MySQL
metadata:
name: my-group
namespace: demo
spec:
authSecret:
name: my-group-auth
podTemplate:
spec:
affinity:
podAntiAffinity:
preferredDuringSchedulingIgnoredDuringExecution:
- podAffinityTerm:
labelSelector:
matchLabels:
app.kubernetes.io/instance: my-group
app.kubernetes.io/managed-by: kubedb.com
app.kubernetes.io/name: mysqls.kubedb.com
namespaces:
- demo
topologyKey: kubernetes.io/hostname
weight: 100
- podAffinityTerm:
labelSelector:
matchLabels:
app.kubernetes.io/instance: my-group
app.kubernetes.io/managed-by: kubedb.com
app.kubernetes.io/name: mysqls.kubedb.com
namespaces:
- demo
topologyKey: failure-domain.beta.kubernetes.io/zone
weight: 50
resources:
limits:
cpu: 500m
memory: 1Gi
requests:
cpu: 500m
memory: 1Gi
serviceAccountName: my-group
replicas: 3
storage:
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 1Gi
storageClassName: standard
storageType: Durable
terminationPolicy: WipeOut
topology:
group:
name: dc002fc3-c412-4d18-b1d4-66c1fbfbbc9b
mode: GroupReplication
version: 8.0.23-v1
status:
observedGeneration: 2$4213139756412538772
phase: Running
Connect with MySQL database
KubeDB operator has created a new Secret called my-group-auth (format: {mysql-object-name}-auth) for storing the password for mysql superuser. This secret contains a username key which contains the username for MySQL superuser and a password key which contains the password for MySQL superuser.
If you want to use an existing secret please specify that when creating the MySQL object using spec.authSecret.name. While creating this secret manually, make sure the secret contains these two keys containing data username and password and also make sure of using root as value of username. For more details see here.
Now, you can connect to this database from your terminal using the mysql user and password.
$ kubectl get secrets -n demo my-group-auth -o jsonpath='{.data.\username}' | base64 -d
root
$ kubectl get secrets -n demo my-group-auth -o jsonpath='{.data.\password}' | base64 -d
dlNiQpjULZvEqo3B
The operator creates a group according to the newly created MySQL object. This group has 3 members (one primary and two secondary).
You can connect to any of these group members. In that case you just need to specify the host name of that member Pod (either PodIP or the fully-qualified-domain-name for that Pod using the governing service named <mysql-object-name>-pods) by --host flag.
# first list the mysql pods list
$ kubectl get pods -n demo -l app.kubernetes.io/instance=my-group
NAME READY STATUS RESTARTS AGE
my-group-0 2/2 Running 1 19m
my-group-1 2/2 Running 0 15m
my-group-2 2/2 Running 1 12m
# get the governing service
$ kubectl get service my-group-pods -n demo
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
my-group-pods ClusterIP None <none> 3306/TCP 137m
# list the pods with PodIP
$ kubectl get pods -n demo -l app.kubernetes.io/instance=my-group -o jsonpath='{range.items[*]}{.metadata.name} ........... {.status.podIP} ............ {.metadata.name}.my-group-pods.{.metadata.namespace}{"\\n"}{end}'
my-group-0 ........... 172.17.0.5 ............ my-group-0.my-group-pods.demo
my-group-1 ........... 172.17.0.6 ............ my-group-1.my-group-pods.demo
my-group-2 ........... 172.17.0.7 ............ my-group-2.my-group-pods.demo
Now you can connect to these database using the above info. Ignore the warning message. It is happening for using password in the command.
# connect to the 1st server
$ kubectl exec -it -n demo my-group-0 -c mysql -- mysql -u root --password=dlNiQpjULZvEqo3B --host=my-group-0.my-group-pods.demo -e "select 1;"
mysql: [Warning] Using a password on the command line interface can be insecure.
+---+
| 1 |
+---+
| 1 |
+---+
# connect to the 2nd server
$ kubectl exec -it -n demo my-group-0 -c mysql -- mysql -u root --password=dlNiQpjULZvEqo3B --host=my-group-1.my-group-pods.demo -e "select 1;"
mysql: [Warning] Using a password on the command line interface can be insecure.
+---+
| 1 |
+---+
| 1 |
+---+
# connect to the 3rd server
$ kubectl exec -it -n demo my-group-0 -c mysql -- mysql -u root --password=dlNiQpjULZvEqo3B --host=my-group-2.my-group-pods.demo -e "select 1;"
mysql: [Warning] Using a password on the command line interface can be insecure.
+---+
| 1 |
+---+
| 1 |
+---+
Check the Group Status
Now, you are ready to check newly created group status. Connect and run the following commands from any of the hosts and you will get the same results.
$ kubectl exec -it -n demo my-group-0 -c mysql -- mysql -u root --password=dlNiQpjULZvEqo3B --host=my-group-0.my-group-pods.demo -e "show status like '%primary%'"
mysql: [Warning] Using a password on the command line interface can be insecure.
+----------------------------------+--------------------------------------+
| Variable_name | Value |
+----------------------------------+--------------------------------------+
| group_replication_primary_member | fc4a4935-e6bf-11ea-bf42-9a7560d22b8f |
+----------------------------------+--------------------------------------+
The value fc4a4935-e6bf-11ea-bf42-9a7560d22b8f in the above table is the ID of the primary member of the group.
$ kubectl exec -it -n demo my-group-0 -c mysql -- mysql -u root --password=MpPhZ9xbVlxvoC4d --host=my-group-0.my-group-pods.demo -e "select * from performance_schema.replication_group_members"
mysql: [Warning] Using a password on the command line interface can be insecure.
+---------------------------+--------------------------------------+-------------------------------+-------------+--------------+-------------+----------------+
| CHANNEL_NAME | MEMBER_ID | MEMBER_HOST | MEMBER_PORT | MEMBER_STATE | MEMBER_ROLE | MEMBER_VERSION |
+---------------------------+--------------------------------------+-------------------------------+-------------+--------------+-------------+----------------+
| group_replication_applier | 768c83e2-e6c0-11ea-bfa5-5a3f7e8f0c23 | my-group-1.my-group-pods.demo | 3306 | ONLINE | SECONDARY | 8.0.23 |
| group_replication_applier | 9ea36443-e6c0-11ea-b4d9-beec0709d261 | my-group-2.my-group-pods.demo | 3306 | ONLINE | SECONDARY | 8.0.23 |
| group_replication_applier | fc4a4935-e6bf-11ea-bf42-9a7560d22b8f | my-group-0.my-group-pods.demo | 3306 | ONLINE | PRIMARY | 8.0.23 |
+---------------------------+--------------------------------------+-------------------------------+-------------+--------------+-------------+----------------+
Data Availability
In a MySQL group, only the primary member can write not the secondary. But you can read data from any member. In this tutorial, we will insert data from primary, and we will see whether we can get the data from any other member.
Read the comment written for the following commands. They contain the instructions and explanations of the commands.
# create a database on primary
$ kubectl exec -it -n demo my-group-0 -- mysql -u root --password=dlNiQpjULZvEqo3B --host=my-group-0.my-group-pods.demo -e "CREATE DATABASE playground;"
mysql: [Warning] Using a password on the command line interface can be insecure.
# create a table
$ kubectl exec -it -n demo my-group-0 -- mysql -u root --password=dlNiQpjULZvEqo3B --host=my-group-0.my-group-pods.demo -e "CREATE TABLE playground.equipment ( id INT NOT NULL AUTO_INCREMENT, type VARCHAR(50), quant INT, color VARCHAR(25), PRIMARY KEY(id));"
mysql: [Warning] Using a password on the command line interface can be insecure.
# insert a row
$ kubectl exec -it -n demo my-group-0 -c mysql -- mysql -u root --password=dlNiQpjULZvEqo3B --host=my-group-0.my-group-pods.demo -e "INSERT INTO playground.equipment (type, quant, color) VALUES ('slide', 2, 'blue');"
mysql: [Warning] Using a password on the command line interface can be insecure.
# read from primary
$ kubectl exec -it -n demo my-group-0 -c mysql -- mysql -u root --password=dlNiQpjULZvEqo3B --host=my-group-0.my-group-pods.demo -e "SELECT * FROM playground.equipment;"
mysql: [Warning] Using a password on the command line interface can be insecure.
+----+-------+-------+-------+
| id | type | quant | color |
+----+-------+-------+-------+
| 7 | slide | 2 | blue |
+----+-------+-------+-------+
In the previous step we have inserted into the primary pod. In the next step we will read from secondary pods to determine whether the data has been successfully copied to the secondary pods.
# read from secondary-1
$ kubectl exec -it -n demo my-group-0 -c mysql -- mysql -u root --password=dlNiQpjULZvEqo3B --host=my-group-1.my-group-pods.demo -e "SELECT * FROM playground.equipment;"
mysql: [Warning] Using a password on the command line interface can be insecure.
+----+-------+-------+-------+
| id | type | quant | color |
+----+-------+-------+-------+
| 7 | slide | 2 | blue |
+----+-------+-------+-------+
# read from secondary-2
$ kubectl exec -it -n demo my-group-0 -c mysql -- mysql -u root --password=dlNiQpjULZvEqo3B --host=my-group-2.my-group-pods.demo -e "SELECT * FROM playground.equipment;"
mysql: [Warning] Using a password on the command line interface can be insecure.
+----+-------+-------+-------+
| id | type | quant | color |
+----+-------+-------+-------+
| 7 | slide | 2 | blue |
+----+-------+-------+-------+
Write on Secondary Should Fail
Only, primary member preserves the write permission. No secondary can write data.
# try to write on secondary-1
$ kubectl exec -it -n demo my-group-0 -c mysql -- mysql -u root --password=dlNiQpjULZvEqo3B --host=my-group-1.my-group-pods.demo -e "INSERT INTO playground.equipment (type, quant, color) VALUES ('mango', 5, 'yellow');"
mysql: [Warning] Using a password on the command line interface can be insecure.
ERROR 1290 (HY000) at line 1: The MySQL server is running with the --super-read-only option so it cannot execute this statement
command terminated with exit code 1
# try to write on secondary-2
$ kubectl exec -it -n demo my-group-0 -c mysql -- mysql -u root --password=dlNiQpjULZvEqo3B --host=my-group-2.my-group-pods.demo -e "INSERT INTO playground.equipment (type, quant, color) VALUES ('mango', 5, 'yellow');"
mysql: [Warning] Using a password on the command line interface can be insecure.
ERROR 1290 (HY000) at line 1: The MySQL server is running with the --super-read-only option so it cannot execute this statement
command terminated with exit code 1
Automatic Failover
To test automatic failover, we will force the primary Pod to restart. Since the primary member (Pod) becomes unavailable, the rest of the members will elect a new primary for these group. When the old primary comes back, it will join the group as a secondary member.
Read the comment written for the following commands. They contain the instructions and explanations of the commands.
# delete the primary Pod my-group-0
$ kubectl delete pod my-group-0 -n demo
pod "my-group-0" deleted
# check the new primary ID
kubectl exec -it -n demo my-group-0 -c mysql -- mysql -u root --password=dlNiQpjULZvEqo3B --host=my-group-0.my-group-pods.demo -e "show status like '%primary%'"
mysql: [Warning] Using a password on the command line interface can be insecure.
+----------------------------------+--------------------------------------+
| Variable_name | Value |
+----------------------------------+--------------------------------------+
| group_replication_primary_member | 4c97e5a4-680a-11e9-9f6b-0242ac110006 |
+----------------------------------+--------------------------------------+
# now check the group status
kubectl exec -it -n demo my-group-0 -c mysql -- mysql -u root --password=dlNiQpjULZvEqo3B --host=my-group-0.my-group-pods.demo -e "select * from performance_schema.replication_group_members"
mysql: [Warning] Using a password on the command line interface can be insecure.
+---------------------------+--------------------------------------+-------------------------------+-------------+--------------+
| CHANNEL_NAME | MEMBER_ID | MEMBER_HOST | MEMBER_PORT | MEMBER_STATE |
+---------------------------+--------------------------------------+-------------------------------+-------------+--------------+
| group_replication_applier | 37ed2c72-680a-11e9-8ac3-0242ac110005 | my-group-0.my-group-pods.demo | 3306 | ONLINE |
| group_replication_applier | 4c97e5a4-680a-11e9-9f6b-0242ac110006 | my-group-1.my-group-pods.demo | 3306 | ONLINE |
| group_replication_applier | 625714bc-680a-11e9-9e94-0242ac110007 | my-group-2.my-group-pods.demo | 3306 | ONLINE |
+---------------------------+--------------------------------------+-------------------------------+-------------+--------------+
# read data from new primary my-group-1.my-group-pods.demo
$ kubectl exec -it -n demo my-group-0 -c mysql -- mysql -u root --password=dlNiQpjULZvEqo3B --host=my-group-1.my-group-pods.demo -e "SELECT * FROM playground.equipment;"
mysql: [Warning] Using a password on the command line interface can be insecure.
+----+-------+-------+-------+
| id | type | quant | color |
+----+-------+-------+-------+
| 7 | slide | 2 | blue |
+----+-------+-------+-------+
Now Let’s read the data from secondary pods to see if the data is consistant.
# read data from secondary-1 my-group-0.my-group-pods.demo
$ kubectl exec -it -n demo my-group-0 -c mysql -- mysql -u root --password=dlNiQpjULZvEqo3B --host=my-group-0.my-group-pods.demo -e "SELECT * FROM playground.equipment;"
mysql: [Warning] Using a password on the command line interface can be insecure.
+----+-------+-------+-------+
| id | type | quant | color |
+----+-------+-------+-------+
| 7 | slide | 2 | blue |
+----+-------+-------+-------+
# read data from secondary-2 my-group-2.my-group-pods.demo
$ kubectl exec -it -n demo my-group-0 -c mysql -- mysql -u root --password=dlNiQpjULZvEqo3B --host=my-group-2.my-group-pods.demo -e "SELECT * FROM playground.equipment;"
mysql: [Warning] Using a password on the command line interface can be insecure.
+----+-------+-------+-------+
| id | type | quant | color |
+----+-------+-------+-------+
| 7 | slide | 2 | blue |
+----+-------+-------+-------+
Cleaning up
Clean what you created in this tutorial.
kubectl delete -n demo my/my-group
kubectl delete ns demo
Next Steps
- Detail concepts of MySQL object.
- Detail concepts of MySQLDBVersion object.
- Want to hack on KubeDB? Check our contribution guidelines.