Extending the cluster

Prerequisites

Before starting this tutorial, complete the Basic tt migrations tutorial and Data migrations with space.upgrade(). As a result, you have a sharded Tarantool EE cluster that uses an etcd-based configuration storage. The cluster has a space with two indexes.

Extending the cluster

Having all migrations in a centralized etcd storage, you can extend the cluster and consistently define the data schema on new instances on the fly.

Add one more storage replica set to the cluster. To do this, edit the cluster files in instances.enabled/myapp:

• instances.yml: add the lines below to the end.

  storage-003-a:
  storage-003-b:
  

• source.yaml: add the lines below to the end.

  storage-003:
    leader: storage-003-a
    instances:
      storage-003-a:
        iproto:
          listen:
          - uri: localhost:3306
          advertise:
            client: localhost:3306
      storage-003-b:
        iproto:
          listen:
          - uri: localhost:3307
          advertise:
            client: localhost:3307
  

Publish the new cluster configuration to etcd:

$ tt cluster publish "http://app_user:config_pass@localhost:2379/myapp/" source.yaml

Run tt start to start up the new instances:

$ tt start myapp
   • The instance myapp:router-001-a (PID = 61631) is already running.
   • The instance myapp:storage-001-a (PID = 61632) is already running.
   • The instance myapp:storage-001-b (PID = 61634) is already running.
   • The instance myapp:storage-002-a (PID = 61639) is already running.
   • The instance myapp:storage-002-b (PID = 61640) is already running.
   • Starting an instance [myapp:storage-003-a]...
   • Starting an instance [myapp:storage-003-b]...

Now the cluster contains three storage replica sets.

Applying migrations to the new replica set

The new replica set – storage-003– is just started and has no data schema yet. Apply all stored migrations to the cluster to load the same data schema to the new replica set:

$ tt migrations apply "http://app_user:config_pass@localhost:2379/myapp" \
                      --tarantool-username=client --tarantool-password=secret
                      --replicaset=storage-003

$ tt migrations apply "http://app_user:config_pass@localhost:2379/myapp" \
                      --tarantool-username=client --tarantool-password=secret

To make sure that the space exists on the new instances, connect to storage-003-a and check box.space.writers:

$ tt connect myapp:storage-003-a

myapp:storage-003-a> box.space.writers ~= nil
---
- true
...