Triggering multi-site replication failover and switchover

You can trigger a failover and switchover when using a Multi‑Site Replication plan.

You can trigger a failover or switchover to redirect traffic to a secondary foundation.

For information about when to trigger a failover or switchover, see About Failover and Switchover.

Before you trigger a failover or switchover, you must verify that the follower service instance is healthy. See Verify Follower Health.

The procedures in this topic assume that you created the leader service instance in the primary foundation and the follower service instance in the secondary foundation.

Verify follower health

Before you trigger a failover or switchover, you must verify that the follower service instance is healthy. If your follower service instance is unhealthy, contact Support.

To verify the service instance:

Log in to the deployment for your secondary foundation by running:
```
cf login SECONDARY-API-URL
```
Where SECONDARY-API-URL is the API endpoint for your secondary foundation.
Record the GUID of the follower service instance by running:
```
cf service SERVICE-INSTANCE-NAME --guid
```
Where SERVICE-INSTANCE-NAME is the name of the follower service instance.

For example:
```
$ cf service my-follower --guid
  12345678-90ab-cdef-1234-567890abcdef
```
Obtain the credentials and IP address needed to SSH into the Tanzu Operations Manager VM by following the procedure in Gather Credential and IP Address Information.
SSH into the Tanzu Operations Manager VM by following the procedure in Log in to the Tanzu Operations Manager VM with SSH.
From the Tanzu Operations Manager VM, log in to your BOSH Director by following the procedure in SSH Into the BOSH Director VM.

View the health of the service instance by running:

bosh -d service-instance_GUID instance

For example:

$ bosh -d service-instance_12345678-90ab-cdef-1234-567890abcdef instance
    Using environment 'https://10.0.0.6:25555' as client 'admin'

    Task 21409. Done

    Deployment 'service-instance_12345678-90ab-cdef-1234-567890abcdef'

    Instance                                    Process State  AZ  IPs
    mysql/1373022d-4eab-46d3-8fd1-a12067edf597  running        z2  10.0.17.14

    1 instances

    Succeeded

Ensure that the service instance is running. If the service instance is failing, contact Support.

Trigger a failover

You can only trigger failover if you do not need to recover the leader service instance.

To trigger a failover:

Promote the Follower
Delete or purge the former leader
Create a Follower
Reconfigure Multi‑Site Replication

Promote the follower

If you try to promote a leader-follower, highly available cluster, or single node service instance to leader or make it read-only, you get an error message similar to:

Updating service instance haDB as admin... FAILED Server error, status code: 502, error code: 10001, message: Service broker error: 1 error occurred: * the configuration parameter 'initiate-failover' is not a valid option

To promote the follower service instance to leader:

Log in to the deployment for your secondary foundation by running:
```
cf login SECONDARY-API-URL
```
Where SECONDARY-API-URL is the API endpoint for your secondary foundation.

Promote the follower service instance to leader by running:

cf update-service SECONDARY-INSTANCE \
-c '{"initiate-failover":"promote-follower-to-leader"}'

For example:

$ cf update-service secondary-node \
  -c '{"initiate-failover":"promote-follower-to-leader"}'

Updating service instance secondary-node as admin...
OK

If this command fails, do one of the following:

If you have unapplied local transactions on the follower service instance, wait for the transactions to be applied and run the command again. The error message looks like the following:

Updating service instance secondary-node as admin...
FAILED
Server error, status code: 502, error code: 10001, message: Service broker error: Promotion of follower failed - has 1 transactions still unapplied

If the leader service instance is still reachable and in read-write mode, follow the procedure in Trigger a Switchover instead. The error message looks like the following:

Updating service instance secondary-node as admin...
FAILED
Server error, status code: 502, error code: 10001, message: Service broker error: Promotion of follower failed - the leader is still writable

Watch the progress of the service instance update by running:

watch cf services

Wait for the last operation for your instance to show as update succeeded.

For example:

$ watch cf services

Getting services in org my-org / space my-space as admin...
OK
name             service       plan                      bound apps    last operation
secondary-node   p.mysql       db-pxc-single-node-small                update succeeded

Reconfigure your global DNS load balancer to direct all traffic to apps in your secondary foundation. See Configure Your GLB.

Delete or purge the former leader

When you do a failover, you cannot manually recover the leader service instance. After you promote the follower service instance to leader, you remove the former leader service instance. Otherwise, the service instance can recover in read-write mode.

The way you remove the service instance, depends on whether the VM has been lost or not.

To remove the former leader service instance:

Log in to the deployment for your primary foundation by running:
```
cf login PRIMARY-API-URL
```
Where PRIMARY-API-URL is the API endpoint for the primary foundation.
Do one of the following:
- If the VM is lost, purge the service instance by doing the procedure Purge a Service Instance in Using VMware SQL with MySQL for Tanzu Application Service.
  If the foundation is lost, you purge the service instance after following the steps to recover the foundation's Cloud Controller database in Restoring Deployments from Backup with BBR.
- If the VM is not lost:
  1. Remove all app bindings by following the procedure Unbind an App from a Service Instance in Using VMware SQL with MySQL for Tanzu Application Service.
  2. Delete the service keys from the former leader service instance.
  3. Delete the service instance by following the procedure Delete a Service Instance in Using VMware SQL with MySQL for Tanzu Application Service.

Create a follower

To reconfigure Multi‑Site Replication between two instances, a new follower without any data must be created in the primary foundation.

To create a follower:

Log in to the deployment for your primary foundation by running:
```
cf login PRIMARY-API-URL
```
Where PRIMARY-API-URL is the API endpoint for the primary foundation.
Create a service instance using the same Multi‑Site Replication plan that was used to create the original instance:
- Follow the procedure in Create a Service Instance in Using VMware SQL with MySQL for Tanzu Application Service.
- Do not name your service instance follower because, if in the future you trigger a failover or switchover, this instance can no longer be the follower.

Reconfigure Multi‑Site Replication

The follower in the primary foundation needs to catch up to the newly promoted leader in the secondary foundation.

Reconfigure Multi‑Site Replication so that the follower in the primary foundation receives the data from the leader in the secondary foundation.

To reconfigure:

Follow the procedure in Reconfigure Multi‑Site Replication.

Trigger a Switchover

To trigger a switchover:

Promote the follower
Reconfigure Multi‑Site Replication

Promote the follower

If you try to promote a leader-follower, highly available cluster, or single node service instance to leader or make it read-only, you get an error message similar to the following:

Updating service instance haDB as admin... FAILED Server error, status code: 502, error code: 10001, message: Service broker error: 1 error occurred: * the configuration parameter 'initiate-failover' is not a valid option

Before you promote the follower service instance, you must make the leader service instance, which is in the primary foundation, a read-only format.

To make the leader read-only and promote the follower to leader in the secondary foundation:

Log in to the deployment for your primary foundation by running:
```
cf login PRIMARY-API-URL
```
Where PRIMARY-API-URL is the API endpoint for the primary foundation.

Set the service instance that is currently the leader to read-only by running:

cf update-service PRIMARY-INSTANCE \
  -c '{"initiate-failover":"make-leader-read-only"}'

For example:

$ cf update-service primary-node \
    -c '{"initiate-failover":"make-leader-read-only"}'

Updating service instance primary-node as admin...
OK

Watch the progress of the service instance update by running:
```
watch cf services
```
Wait for the last operation for your instance to show as update succeeded.
Log in to the deployment for your secondary foundation by running:
```
cf login SECONDARY-API-URL
```
Where SECONDARY-API-URL is the API endpoint for your secondary foundation.

Promote the service instance in the secondary foundation to leader by running:

cf update-service SECONDARY-INSTANCE \
  -c '{"initiate-failover":"promote-follower-to-leader"}'

If this command fails, do one of the following:

If you have unapplied local transactions on the follower service instance, wait for the transactions to be applied and then run the command again. The error message might look like the following:

Updating service instance secondary-node as admin...
FAILED
Server error, status code: 502, error code: 10001, message: Service broker error: Promotion of follower failed - has 1 transactions still unapplied

If the leader service instance is still reachable and in read-write mode, follow the procedure in Trigger a Switchover instead. The error message might look like the following:

Updating service instance secondary-node as admin...
FAILED
Server error, status code: 502, error code: 10001, message: Service broker error: Promotion of follower failed - the leader is still writable

Watch the progress of the service instance update by running:
```
watch cf services
```
Wait for the last operation for your instance to show as update succeeded.

Reconfigure Multi‑Site Replication

To establish a connection between the service instances in the primary and secondary foundations, you must reconfigure replication. Reconfiguring replication is similar to the procedure in Configure multi‑site replication except the service instance in the primary foundation is the follower and the service instance in the secondary foundation is the leader.

Caution To successfully trigger a switchover, the follower dataset must be a subset of the leader dataset. This means that VMware SQL with MySQL for TAS has not written new data to the follower. The follower must also be no more than 3 days behind the leader.

If your follower instance does not satisfy these requirements, you must create a new Multi‑Site Replication service instance and reconfigure replication using this new, empty instance as the follower.

Workflow for reconfiguring Multi‑Site Replication

The following diagram describes the workflow for reconfiguring multi-site replication:

alt-text=Two boxes labeled Primary Foundation and Secondary Foundation.
Six steps are shown. Steps 1 and 2 are in Primary Foundation;
Steps 3, 4, and 5 are in Secondary Foundation,
and Step 6 is in Primary Foundation.

The steps shown in the diagram are:

Create host-info service key.
Record host-info service key.
Update secondary service instance with host-info service key.
Create credentials service key.
Record credentials service key.
Update primary service instance with credentials service key.

Procedure for reconfiguring Multi‑Site Replication

To reconfigure replication for the service instances:

Create a host-info service key for the service instance in your primary foundation:

cf create-service-key PRIMARY-INSTANCE SERVICE-KEY \
  -c '{"replication-request": "host-info"}'

Where:

PRIMARY-INSTANCE is the name of the follower service instance in the primary foundation.
SERVICE-KEY is a name you choose for the host-info service key.

For example:

$ cf create-service-key primary-node host-info \
      -c '{"replication-request": "host-info" }' 

Creating service key host-info for service instance primary-node as admin...
OK

View the replication-credentials for your host-info service key by running:

cf service-key PRIMARY-INSTANCE SERVICE-KEY

Where:

PRIMARY-INSTANCE is the name of the follower service instance in the primary foundation.
SERVICE-KEY is the name of the host-info service key you created in previous step.

For example:

$ cf service-key primary-node host-info-key 

Getting key host-info-key for service instance primary-node as admin...

  {
    "credentials": {
        "replication": {
            "peer-info": {
              "hostname": "primary.bosh",
              "ip": "10.0.19.12",
              "system_domain": "sys.primary-domain.com",
              "uuid": "ab12cd34-5678-91e2-345f-67891h234567"
          },
          "role": "leader"
        }
    }
  }

Caution
In cf CLI v8, the response includes a top-level credentials key. Earlier versions of the cf CLI do not include a top-level credentials key. This procedure assumes that you are using cf CLI v8.

Record the output of the previous command, and remove the top-level credentials key.
Log in to the deployment for your secondary foundation by running:
```
cf login SECONDARY-API-URL
```

Update your leader service instance in the secondary foundation with the host-info service key by running:

cf update-service SECONDARY-INSTANCE -c HOST-INFO

Where:

SECONDARY-INSTANCE is the name of the primary service instance you created in step 1 of Creating Multi‑Site Replication service instances.
HOST-INFO is the output you recorded in step 3.

For example:

$ cf update-service primary-node -c '{
"replication":{ \
  "peer-info":{ \
      "hostname": "primary.bosh", \
      "ip": "10.0.18.12", \
      "system_domain": "sys.primary-domain.com", \
      "uuid": "ab12cd34-5678-91e2-345f-67891h234567" \
    },\
  "role": "leader" \
  } \
}'

Updating service instance primary-node as admin...
OK

Monitor the progress of the service instance update by running:
```
watch cf services
```
Wait for the last operation for your instance to show as update succeeded.
Create a credentials service key for the service instance in your secondary foundation by running:
```
cf create-service-key SECONDARY-INSTANCE SERVICE-KEY-NAME \
  -c '{"replication-request": "credentials"}'
```
Where:
- SECONDARY-INSTANCE is the name of the service instance in the secondary foundation.
- SERVICE-KEY-NAME is a name you choose for the credentials service key.
For example:
```
$ cf create-service-key secondary-node cred-key \
    -c '{"replication-request": "credentials" }'

Creating service key cred-key for service instance secondary-node as user@example.com...
OK
```
The -c flag is different than the one in step 2.

View the replication-credentials for your credentials service key by running:

cf service-key SECONDARY-INSTANCE SERVICE-KEY-NAME

Where:

SECONDARY-INSTANCE is the name of the leader service instance in the secondary foundation.
SERVICE-KEY-NAME is the name of the credentials service key you created in step 7.

For example:

$ cf service-key secondary-node cred-key 

Getting key cred-key for service instance secondary as admin...

  {
    "credentials": {
        "replication": {
          "credentials": {
            "password": "a22aaa2a2a2aaaaa",
            "username": "6bf07ae455a14064a9073cec8696366c"
          },
          "peer-info": {
            "hostname": "secondary.bosh",
            "ip": "10.0.17.12",
            "system_domain": "sys.secondary-domain.com",
            "uuid": "zy98xw76-5432-19v8-765u-43219t876543",
            "ports": {
                "mysql":  3306,
                "agent":  8443,
                "backup": 8081   
           }, 
          },
          "role": "follower"
        }
    }
  }

Caution
In cf CLI v8, the response includes a top-level credentials key. Earlier versions of the cf CLI do not include a top-level credentials key. This procedure assumes that you are using cf CLI v8.

Record the output of the previous command, and remove the top-level credentials key.
Log in to the deployment for your primary foundation by running:
```
cf login PRIMARY-API-URL
```

Update the follower service instance in the primary foundation with the credentials service key by running:

cf update-service PRIMARY-INSTANCE -c CREDENTIALS

Where:

PRIMARY-INSTANCE is name of the follower service instance in the primary foundation.
CREDENTIALS is the output you recorded in the previous step.

For example:

$ cf update-service primary-node -c '{"replication": { \
    "credentials": { \
      "password": "a22aaa2a2a2aaaaa", \
      "username": "6bf07ae455a14064a9073cec8696366c" \
    }, \
    "peer-info": { \
      "hostname": "secondary.bosh", \
      "ip": "10.0.17.12", \
      "system_domain": "sys.secondary-domain.com", \
      "uuid": "zy98xw76-5432-19v8-765u-43219t876543", \
      "ports": { \
        "mysql":  3306, \
        "agent":  8443, \
        "backup": 8081  \
       }, \
    }, \
    "role": "follower" \
  } \
}'

Updating service instance primary-node as admin...
OK

Watch the progress of the service instance update by running:

watch cf services

Wait for the last operation for your instance to show as update succeeded.

You now have a leader-follower service instance successfully configured, where the leader is in your secondary foundation and your follower is in the primary foundation.

If this command fails and you get one of the following errors, you must create a new Multi‑Site Replication service instance and reconfigure replication using this new, empty instance as the follower.

If your follower service instance is more than 3 days behind leader, you get error message similar to the following:

$ cf update-service primary-node -c /tmp/credentials-key.json
Updating service instance primary-node as admin...
FAILED
Server error, status code: 502, error code: 10001, message: Service broker error: Establishing Replication Failed - follower is too far behind Leader to start replication
Leader GTIDs offering: "487e6056-6e93-11ea-8c96-42010a010806:5-9"
Follower GTIDs missed: "487e6056-6e93-11ea-8c96-42010a010806:1-9"
Try again with an empty instance or contact your operator to troubleshoot

If your follower has a divergent dataset from the leader, you get error message similar to the following:

$ cf update-service primary-node -c /tmp/credentials-key.json
Updating service instance primary-node as admin...
FAILED
Server error, status code: 502, error code: 10001, message: Service broker error: Establishing Replication Failed - the follower has divergent data
Leader GTIDs applied: "bd2ff185-6947-11ea-80d8-42010a000808:1-20"
Follower GTIDs applied: "c1abd2a4-6947-11ea-8099-42010a010807:1-15"
Try again with an empty instance or contact your operator to troubleshoot

In either case, you must create a new multi-site service instance and reconfigure replication using this new, empty instance as the follower.

Reconfigure your global DNS load balancer to direct traffic to the correct foundations of your choice. See Configure Your GLB.