umzug-sync

Sequelize (Postgresql only) migrations for distributed systems. This library uses umzug, the library used by Sequelize to run migrations. Usually those migrations are run from the command line tool, sequelize-cli. This library makes it easy and safe to run migrations from the application code across a cluster of servers. All servers can call usync.migrate() and wait on the promise and be guaranteed upon resolution that the database schema is fully up to date.

Umzug-sync is resilient against race conditions, conflicts, concurrent migrations, timeouts and many other issues that may occur in distributed environments.

``js
var usync = require('umzug-sync')
var Sequelize = require('sequelize')
var sequelize = new Sequelize({ / sequelize options / })

var config = {
sequelize: sequelize,
SequelizeImport: Sequelize,
migrationsDir: 'migrations/'
}

usync.migrate(config)
.then(function () {
// Execute program
})
.catch(function (err) {
// Handle the error, something bad happened
})
`

There is only one function: migrate(). It takes a config object and returns a promise.

$3

The config object supports the following options:

| Name | Type | Mandatory | Default | Description |
|------|------|-----------|---------|-------------|
| sequelize | Object | Yes | | A configured instance of Sequelize. |
| SequelizeImport | Object | Yes | | The Sequelize library object that created the sequelize instance. |
| migrationsDir | String | Yes | | Path (relative or absolute) where the migration files are located. Those files must end in .js. |
| chdir | String | No | | Sometimes migration files load other files relatively to a certain assumed Current Working Directory (cwd/pwd). Setting this option to a path will change the cwd/pwd of the process for the duration of the migrate() function execution and change it back afterwards. |
| logging | Function | No | | Function that will be called with a single string argument whenever a migration event occurs. Example value: console.log |
| timeout | Integer | No | 15 | Maximum time (in seconds) to wait for the mutex. migrate() is guaranteed to resolve/reject within 2 * timeout |

$3

Race conditions are possible if the timeout expires before the migrations are done executing. This is by design in case a migration gets "jammed" or the server simply disappears mid-migration(s). This way another server will get a chance to run the migrations instead of leaving the whole system in a broken state. So pick the timeout` value carefully.