Migrations manager for Tarantool Cartridge

@lookup README.md

Migrations module allows you to run cluster-wide migrations for your data.

It stores the list of applied migrations in cluster-wide config and applies resulting schema to cartridge ddl.

Usage

Add migrations dependency:

-- <project-name>-scm-1.rockspec
    dependencies = {
        ...
        'migrations == <the-latest-tag>-1',
        ...
    }

Add migrator to the list of cartridge roles in init.lua:

-- init.lua
....
cartridge.cfg({
  roles = {
    'migrator',
    ....
  }
})

Put migrations code to ./migrations folder in your app. By default, migrator loads all files from it using lexicographical order. Every migration (e. g. 0001_create_my_sharded_space_DATETIME.lua) should expose a single parameter-less function up:

return {
    up = function()
    local utils = require('migrator.utils')
    local f = box.schema.create_space('my_sharded_space', {
        format = {
            { name = 'key', type = 'string' },
            { name = 'bucket_id', type = 'unsigned' },
            { name = 'value', type = 'any', is_nullable = true }
        },
        if_not_exists = true,
    })
    f:create_index('primary', {
        parts = { 'key' },
        if_not_exists = true,
    })
    f:create_index('bucket_id', {
        parts = { 'bucket_id' },
        if_not_exists = true,
        unique = false
    })
    utils.register_sharding_key('my_sharded_space', {'key'})
    return true
    end
}

Call curl -X POST http://<your_tarantool_ip>:<http_port>/migrations/up once you are ready to migrate or connect to any instance of cluster and call require('migrator').up().
What will happen then:
- coordinator node (the one you curled upon) will trigger migrations execution on all replicaset leaders;
- each replicaset leader will apply all available migrations and reply to coordinator;
- each replicaset leader stores a list of applied migrations in a space;
- if all replies are successful, coordinator will apply changes to the resulting cluster ddl-schema.
That's it!

Advanced usage

IMPORTANT: code snippets below should be embedded to init.lua, so they would take effect on all nodes of the cluster.

Change directory where migrations are located: embed the following to init.lua

local migrator = require('migrator')
local my_directory_loader = require('migrator.directory-loader').new('test/integration/migrations')
migrator.set_loader(my_directory_loader)

... or use migrator.config-loader to load migrations from Tarantool Cartridge clusterwide config.

Configure migrator to use config-loader:
```
local migrator = require('migrator')
local config_loader = require('migrator.config-loader').new()
migrator.set_loader(config_loader)
```
Navigate to Cartridge webui "Code" to write your migrations. Migrations must be stored in *.lua files under "migrations/source" key:

... or use your own loader - it should expose a single function list(self) which returns a similar-looking array:

local my_loader = {
    list = function(_)
        return {
            {
                name  = '01_first',
                up = function() ... end
            },
        }
    end
}
migrator.set_loader(my_loader)

Disable cartridge.ddl usage:
```
migrator.set_use_cartridge_ddl(false)
```
In this case, resulting schema will not be registered via cartridge_set_schema

Utils, helpers, tips and tricks

Specify a sharding key for cartridge.ddl (if you use it) using utils.register_sharding_key:

    up = function()
        local utils = require('migrator.utils')
        local f = box.schema.create_space('my_sharded_space', {
            format = {
                { name = 'key', type = 'string' },
                { name = 'bucket_id', type = 'unsigned' },
                { name = 'value', type = 'any', is_nullable = true }
            },
            if_not_exists = true,
        })
        f:create_index('primary', {
            parts = { 'key' },
            if_not_exists = true,
        })
        f:create_index('bucket_id', {
            parts = { 'bucket_id' },
            if_not_exists = true,
            unique = false
        })
        utils.register_sharding_key('my_sharded_space', {'key'})
        return true
    end

Warning! It's not correct to specify 'bucket_id' as a 'key' parameter for register_sharding_key(). The 'bucket_id' field is a place where the output of sharding function is saved to.

Before 0.6.0, each storage migration run time was limited to 3600 seconds (#66). If your migrations run longer than this limit, it will result in timeout error.

Starting with 0.6.0, you may configure this value with clusterwide config to allow longer migrations. Default is 3600 seconds.
```
migrations:
  options:
    storage_timeout: 43200 # in seconds
```

To run migrations code on a specific roles use utils.check_roles_enabled:

    up = function()
        local utils = require('migrator.utils')
        if utils.check_roles_enabled({'vshard-storage'}) then
            local f = box.schema.create_space('my_sharded_space', {
                format = {
                    { name = 'key', type = 'string' },
                    { name = 'bucket_id', type = 'unsigned' },
                    { name = 'value', type = 'any', is_nullable = true }
                },
                if_not_exists = true,
            })
            f:create_index('primary', {
                parts = { 'key' },
                if_not_exists = true,
            })
            f:create_index('bucket_id', {
                parts = { 'bucket_id' },
                if_not_exists = true,
                unique = false
            })
            utils.register_sharding_key('my_sharded_space', {'key'})
            return true
        elseif utils.check_roles_enabled({'my-role'}) then
            my_specific_role_logic()
        end
    end

To get a list of applied migrations make a GET request to http://<your_tarantool_ip>:<http_port>/migrations/applied or call require('migrator').get_applied() on any cluster instance. This method will return a list of applied migrations grouped by a leader node.

Upgrade from 0.* versions.

Applied migrations names storage method has been changed in 1.* version: applied migrations list is stored on each cluster node separately in _migrations space. An additional step is required before applying migrations after update from 0.*: call curl -X POST http://<your_tarantool_ip>:<http_port>/migrations/move_migrations_state or connect to any instance of cluster and call require('migrator').move_migrations_state(). This method does the following:

copies applied migrations names from cluster-wide configuration to the _migrations space on leader nodes.
if copying is succeeded on all leaders, removes the list from the cluster-wide configuration.

Rolling back to 0.* versions.

To perform a downgrade from 1.* to 0.* version do the following:

get a list of the applied migrations using the get_applied API.
set list of migrations in cluster-wide config:

    migrations:
      applied:
      - 01_migration.lua
      - 02_migration.lua
      . . .

remove _migrations space and _migrations_id_seq on all nodes if necessary.
perform downgrade of the migrations.

Limitations

all migrations will be run on all cluster nodes (no partial migrations);
no pre-validation for migrations code (yet), so you should test them beforehands;
no support to run a single migration (yet);
no dry-run (yet);
no rolling back unsuccessful migrations (yet);
no migrating down (yet).