Create replica databases on Kubernetes

How to create and automate database replicas using the database controller

You can configure a replica of a database by creating an item in the replicaSources section of the Redis Enterprise database specification. The value of replicaSourceType must be 'SECRET'; replicaSourceName must be the name of a secret that contains the replica source url.

A secret must be created using a stringData section containing the replica source URI as follows:

apiVersion: v1
kind: Secret
metadata:
   name: my-replica-source
stringData:
   uri: replica-source-uri-goes-here

The replica source URL can be retrieved by going to "UI > database > configuration > Press the button Get Replica of source URL" in the administrative UI. But, this information can also be retrieved directly from the REST API as well.

A replica of database CR simply uses the secret in the replicaSources section:

apiVersion: app.redislabs.com/v1alpha1
kind: RedisEnterpriseDatabase
metadata:
   name: name-of-replica
spec:
   redisEnterpriseCluster:
      name: name-of-cluster
   replicaSources:
   - replicaSourceType: SECRET
     replicaSourceName: my-replica-source

In the above, name-of-replica database will be created as a replica of the source database as long as the source database exists on the source cluster and the secret contains the correct replica source URL for that database.

Retrieving the replica source URL via kubectl

You will need kubectl, curl, and jq installed for this procedure.

  1. Set your metadata:

    CLUSTER_NAME=test
SOURCE_DB=db1
TARGET_DB=db2
TARGET_CLUSTER_NAME=test

  2. Retrieve the cluster authentication:

    CLUSTER_USER=`kubectl get secret/${CLUSTER_NAME} -o json | jq -r .data.username | base64 -d`
CLUSTER_PASSWORD=`kubectl get secret/${CLUSTER_NAME} -o json | jq -r .data.password | base64 -d`

  3. Forward the port of the REST API service for your source cluster:

    kubectl port-forward pod/${CLUSTER_NAME}-0 9443

  4. Request the information from the REST API:

    JQ='.[] | select(.name=="'
JQ+="${SOURCE_DB}"
JQ+='") | ("redis://admin:" +  .authentication_admin_pass + "@"+.endpoints[0].dns_name+":"+(.endpoints[0].port|tostring))'
URI=`curl -sf -k -u "$CLUSTER_USER:$CLUSTER_PASSWORD" "https://localhost:9443/v1/bdbs?fields=uid,name,endpoints,authentication_admin_pass" | jq "$JQ" | sed 's/"//g'`

    Note: URI now contains the replica source URI.

  5. Construct the secret for the replica:

    cat << EOF > secret.yaml
apiVersion: v1
kind: Secret
metadata:
  name: ${SOURCE_DB}-url
stringData:
  uri: ${URI}
EOF
kubectl apply -f secret.yaml

  6. Create the replica database:

    cat << EOF > target.yaml
apiVersion: app.redislabs.com/v1alpha1
kind: RedisEnterpriseDatabase
metadata:
  name: ${TARGET_DB}
spec:
  redisEnterpriseCluster:
    name: ${TARGET_CLUSTER_NAME}
  replicaSources:
  - replicaSourceType: SECRET
    replicaSourceName: ${SOURCE_DB}-url
EOF
kubectl apply -f target.yaml

Automating the creation via a job

The following procedure uses a ConfigMap and a Job to construct the replica source URL secret from the source database and configure the target database.

There are four parameters:

  • source - the name of the source database
  • cluster - the name of the cluster for the source database
  • target - the name of the target database
  • targetCluster - the name of the cluster for the target database

These parameters can be set by:

kubectl create configmap replica-of-database-parameters \
--from-literal=source=name-of-source \
--from-literal=cluster=name-of-cluster \
--from-literal=target=name-of-target \
--from-literal=targetCluster=name-of-cluster

where "name-of-..." is replaced with the database source, source cluster, database target, and target cluster names.

The Job and ConfigMap below, when submitted, will create the secret and replica database:

apiVersion: batch/v1
kind: Job
metadata:
  name: replica-of-database
spec:
  backoffLimit: 4
  template:
    spec:
      serviceAccountName: redis-enterprise-operator
      restartPolicy: Never
      volumes:
        - name: scripts
          configMap:
            name: replica-of-database
      containers:
        - name: createdb
          image: debian:stable-slim
          env:
            - name: MY_NAMESPACE
              valueFrom:
                fieldRef:
                  fieldPath: metadata.namespace
            - name: SCRIPT
              value: create.sh
            - name: SOURCE_DB
              valueFrom:
                configMapKeyRef:
                  name: replica-of-database-parameters
                  key: source
            - name: TARGET_DB
              valueFrom:
                configMapKeyRef:
                  name: replica-of-database-parameters
                  key: target
            - name: CLUSTER_SERVICE
              value: .svc.cluster.local
            - name: CLUSTER_NAME
              valueFrom:
                configMapKeyRef:
                  name: replica-of-database-parameters
                  key: cluster
            - name: CLUSTER_PORT
              value: "9443"
            - name: TARGET_CLUSTER_NAME
              valueFrom:
                configMapKeyRef:
                  name: replica-of-database-parameters
                  key: targetCluster
          volumeMounts:
            - mountPath: /opt/scripts/
              name: scripts
          command:
            - /bin/bash
            - -c
            - |
              apt-get update; apt-get install -y curl jq apt-transport-https gnupg2
              apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 6A030B21BA07F4FB
              curl -s https://packages.cloud.google.com/apt/doc/apt-key.gpg | apt-key add -
              echo "deb https://apt.kubernetes.io/ kubernetes-xenial main" | tee -a /etc/apt/sources.list.d/kubernetes.list
              apt-get update
              apt-get install -y kubectl
              bash /opt/scripts/$SCRIPT              
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: replica-of-database
data:
  create.sh: |
    CLUSTER_USER=`kubectl get secret/${CLUSTER_NAME} -o json | jq -r .data.username | base64 -d`
    CLUSTER_PASSWORD=`kubectl get secret/${CLUSTER_NAME} -o json | jq -r .data.password | base64 -d`
    CLUSTER_HOST=${CLUSTER_NAME}.${MY_NAMESPACE}${CLUSTER_SERVICE}
    JQ='.[] | select(.name=="'
    JQ+="${SOURCE_DB}"
    JQ+='") | ("redis://admin:" +  .authentication_admin_pass + "@"+.endpoints[0].dns_name+":"+(.endpoints[0].port|tostring))'
    URI=`curl -sf -k -u "$CLUSTER_USER:$CLUSTER_PASSWORD" "https://${CLUSTER_HOST}:${CLUSTER_PORT}/v1/bdbs?fields=uid,name,endpoints,authentication_admin_pass" | jq "$JQ" | sed 's/"//g'`
    echo "URL: ${URL}"
    echo ""
    cat << EOF > /tmp/secret.yaml
    apiVersion: v1
    kind: Secret
    metadata:
      name: ${SOURCE_DB}-url
    stringData:
      uri: ${URI}
    EOF
    cat /tmp/secret.yaml
    cat << EOF > /tmp/target.yaml
    apiVersion: app.redislabs.com/v1alpha1
    kind: RedisEnterpriseDatabase
    metadata:
      name: ${TARGET_DB}
    spec:
      redisEnterpriseCluster:
        name: ${TARGET_CLUSTER_NAME}
      replicaSources:
      - replicaSourceType: SECRET
        replicaSourceName: ${SOURCE_DB}-url
    EOF
    echo "---"
    cat /tmp/target.yaml
    echo ""
    kubectl -n ${MY_NAMESPACE} apply -f /tmp/secret.yaml
    kubectl -n ${MY_NAMESPACE} apply -f /tmp/target.yaml
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