One Table to Rule Them All

DynamoDB OneTable Migration Library

This library provides migrations support for DynamoDB OneTable.

OneTable migrations can be executed locally for simple tasks, however it is best to host your migrations close to the DynamoDB table for maximum performance. When executing locally, the migration scripts reside on your local computer and DynamoDB operations are performed from your system. When executing remotely, the migration scripts reside in your AWS account region and DynamoDB operations are performed there, in close proximity to the DynamoDB table.

You should generally host this library and migrations to execute in the same AWS region and availability zone as your DynamoDB table. This will accelerate migrations by minimizing the I/O transfer time.

The easiest way to remotely host this library is by deploying the OneTable Controller which is an easy to deploy, complete solution for remote hosting.

Use the OneTable CLI which relies on this library if you want command control of migrations.

Use the SenseDeep DynamoDB Developer Studio which provides a graphical DynamoDB migration manager that uses this library.

OneTable Migration Features

• Mutate database schema and contents via discrete, reversible migrations.
• Migrate upwards, downwards, to specific versions.
• Automated, ordered sequencing of migrations in both directions.
• Named migrations for database maintenance, auditing and other tasks.
• Add and remove seed data in any migration.
• Quick reset of DynamoDB databases for development.
• Show database status and list applied migrations.
• Show outstanding migrations.
• Stored history of migrations.
• Persist migration history and the current OneTable schema in the table.
• Control by the SenseDeep DynamoDB Developer Studio GUI.
• No module dependencies other than OneTable.
• Supported by SenseDeep for graphical migrations control.
• Works with AWS SDK v2 and v3

Installation

npm i onetable-migrate

Quick Tour

Import the library:

import {Table} from 'dynamodb-onetable'
import {Migrate} from 'onetable-migrate'

or

const {Table} = require('dynamodb-onetable')
const {Migrate} = require('onetable-migrate')

Initialize the Migrate instance with a OneTable Table instance using the AWS SDK v2 DocumentClient.

For initialization using the AWS SDK v3, see the OneTable Documentation.

const OneTableParams = {
    client: new DynamoDBClient(),
    name: 'MyTable',
})
const migrate = new Migrate(OneTableParams, params)
await migrate.init()

See the OneTable documentation for details of the Table constructor and other OneTable configuration parameters.

The Migrate params provides a list of migrations as either:

• A directory containing migration source files, or
• A list of in-memory migrations

For example:

const migrate = new Migrate(OneTableParams, {dir: './migrations'})
await migrate.init()

where the migrations look like:

export default {
    description: 'Initial Migration',
    version: '0.0.1',
    schema: Schema,

    async up(db, migrate, params) {
        if (!params.dry) {
            await db.create('Status', {})
        }
    },

    async down(db, migrate, params) {
        if (!params.dry) {
            await db.remove('Status', {})
        }
    },
}

or via in-memory migrations:

const migrate = new Migrate(OneTableParams, {
    migrations: [
        {
            version: '0.0.1',
            description: 'Initialize the database',
            schema: Schema,
            async up(db, migrate, params) {
                if (!params.dry) {
                    await db.create('Status', {})
                } else {
                    console.log('DRY: create "Status"')
                }
            },
            async down(db, migrate, params) {
                if (!params.dry) {
                    await db.remove('Status', {})
                } else {
                    console.log('DRY: create "Status"')
                }
            },
        },
    ],
})
await migrate.init()

Note: migrations must have a version and schema properties. The schema is the OneTable schema that applies at this version.

If params is not provided, it defaults to looking for migrations in the current directory. i.e. params of {dir: '.'}.

Migrate Examples

import {Migrate} from 'onetable-migrate'

//  See above example for Migrate parameters
const migrate = new Migrate(OneTableParams, {dir: './migrations'})

//  Initialize the migration library. This reads the table primary keys.
await migrate.init()

//  Apply a specific migration. The first parameter is an action: "up", "down", "repeat" 
let migration = await migrate.apply("up", '0.0.1', {dry: false})

//  Apply a named migration. 
let migration = await migrate.apply("cleanup-orphans")
let migration = await migrate.apply("reset")

//  Return a list of applied migrations
let migrations = await migrate.getPastMigrations()

//  Get the last applied migration
let version = await migrate.getCurrentVersion()

//  Get a list of outstanding migrations
let outstanding = await migrate.getOutstandingVersions()

Migrations will save a history of migrations in the database. This will include the current OneTable schema.

The Migration history will be saved as items using the _Migration model using the _migrations: primary hash key value. NOTE: the : delimiter is always used regardless of the OneTable delimiter setting.

The Schema will be saved as a single item using the _Schema model using the _schema primary hash key value.

Migrate Constructor

The Migrate constructor takes the following parameters:

Property	Type	Description
config	Table|map	A OneTable Table instance OneTable or a map of OneTable properties.
params	map	Hash containing migrations or dir properties

The params property may contain either:

• dir path property describing a directory containing migration files.
• migrations array containing maps that describe each migration.
• dry boolean Run in dry-run mode where the migration scripts are invoked and params.dry is set to true.

The migrations array contains an ordered set of migrations of the form:

{
    version: 'x.y.z',
    description: 'Migration Description',
    schema: Schema,

    async up(db, migrate, params) {
        //  Code to upgrade the database
    },
    async down(db, migrate, params) {
        //  Code to downgrade the database to the prior version
        if (!params.dry) {
            await db.remove('Status', {})
        }
    }
}

For versioned migrations, the version should be a SemVer compatible version. For named migrations, the version should be set to the migration name and must not be a SemVer compatible string.

The up and down functions receive the OneTable Table instance via the db parameter. The migrate parameter is the Migrate instance. You can access the parameters provided to onetable-migrate via migrate.params.

Each migration must reference the Schema that applies to that version of the database. The Migrate library saves the current schema to the database so that tooling and always understand the stored data. The migration must specify a version property.

Reset Migration

You can create a special reset named migration that is used for the CLI migrate reset command which is is a quick way to get a development database up to the current version. For the reset migration, the version field should be set to reset.

The reset migration should remove all data from the database and then initialize the database equivalent to applying all migrations.

When creating your reset.js migration, be very careful when removing all items from the database. We typically protect this with a test against the deployment profile to ensure you never do this on a production database.

Sample reset.js migration:

const migrate = new Migrate(OneTableParams, {
    migrations: [
        {
            version: 'reset',
            description: 'Database reset',
            schema: Schema,
            async up(db, migrate, params) {
                if (!params.dry) {
                    if (migrate.params.profile == 'dev') {
                        await removeAllItems(db)
                    }
                }
                //  Provision required database data
            },
            async down(db, migrate, params) {
                if (!params.dry) {
                    if (migrate.params.profile == 'dev') {
                        await removeAllItems(db)
                    }
                }
            },
        },
    ],
})
await migrate.init()

async function removeAllItems(db) {
    do {
        items = await db.scanItems({}, {limit: 100})
        for (let item of items) {
            await db.deleteItem(item)
        }
    } while (items.length)
}

Named Migrations

Named migrations are useful for maintenance tasks that need to be performed on a periodic basis.

A named migration has a migration version property set to a name that is not a valid SemVer version. Named migrations will be excluded from the list of outstanding or past migrations.

Migrate Methods

async apply(action, version, params)

Apply or revert a migration. The action parameter may be set to "up" for upgrades, "down" for downgrades, "repeat" to re-apply the latest migration or any named migration including "reset".

The version is the destination version for upgrdes and downgrades. All intermediate migrations will be applied or reverted to reach the destination. Note: when you upgrade to a version, the "up" routine of that migration version will be run. When you downgrade to a version, all the "down" routines above that target version will be run in sequence, but the target version's "down" routine will not be called.

The params are provided to the up/down functions. The params.dry will be true to indicate it should be a dry-run and not perform any descructive updates to the table.

async getCurrentVersion()

Returns the current migration version. This is the last migration that was applied and has not been reverted.

async getNamedVersions()

Returns a list of available named migrations verions. This returns a simple list of named migrations name.

async getOutstandingVersions()

Returns a list of versions that have not yet been applied.

async getOutstandingMigrations()

Returns a list of migrations that have not yet been applied.

async getPastMigrations()

Returns a list of all migrations that have been applied (and not reverted). The result is a list of migration objects.

async getPastVersions()

Returns a list of all SemVer migrations that have been applied (and not reverted). The result is a simple list of version strings.

async init()

Initialize the migration library. This reads the table keys. This MUST be called after constructing the Migrate instance.

Deployment

You use deploy this library two ways:

• Local Migrations via the OneTable CLI.
• Remote Migrations hosted via Lambda and remotely controlled via the OneTable CLI.

Local Migrations

With local migrations, you keep your migration scripts locally on a development system and manage using the OneTable CLI. The OneTable CLI includes this migration library internally and can manage migrations using AWS credentials.

The migration scripts must be JavaScript. TypeScript migrations must be compiled to Javascript for execution.

In this mode, DynamoDB I/O is performed from within the OneTable CLI process. This means I/O travels to and from the system hosting the OneTable CLI process. This works well for local development databases and smaller remote databases.

Remote Migrations

If you have production databases or complex migrations, you should host the OneTable Migrate library via AWS Lambda so that it executes in the same AWS region and availablity zone as your DynamoDB instance. This will accelerate migrations by minimizing the I/O transfer time.

The OneTable Controller sample is an self-contained sample hosting of this library for executing migrations in the cloud. It uses the serverless framework to create a Lambda proxy that responds to CLI and SenseDeep migration commands.

The OneTable CLI can control your migration lambda when operating in proxy mode by setting the arn of your migration Lambda.

Lambda Hosting

When hosted remotely, a Lambda function receives proxied commands from the OneTable CLI and relays to the OneTable Migrate library API.

The OneTable CLI should be configured with the ARN of the Lambda function in the migrate.json arn property. Access should be controlled via suitable IAM access credentials that are passed to the OneTable CLI via the command line or via the migrate.json aws properties. See OneTable CLI for more details.

Here is a sample Lambda hosting of OneTable Migrate:

import {Migrate} from 'onetable-migrate'
import DynamoDB from 'aws-sdk/clients/dynamodb'

// AWS SDK V3
let client = new DynamoDBClient({})

//  AWS SDK V2
// let client = new DynamoDB.DocumentClient()

exports.handler = async (event, context) => {
    let {action, args, config, dry} = event

    config.client = client
    let migrate = new Migrate(config, {dir: './migrations'})
    await migrate.init()

    let data

    switch (action) {
        case 'apply':
            let {action, version, params} = args
            data = await migrate.apply(action, version, params)
            break
        case 'getCurrentVersion':
            data = await migrate.getCurrentVersion()
            break
        case 'getPastMigrations':
            data = await migrate.getPastMigrations()
            break
        case 'getOutstandingVersions':
            data = await migrate.getOutstandingVersions()
            break
        case 'getOutstandingMigrations':
            data = await migrate.getOutstandingMigrations()
            break
        case 'getNamedVersions':
            data = await migrate.getNamedVersions()
            break
        default:
            throw new Error(`Unknown migration action ${action}`)
    }
    return {
        body: data,
        statusCode: 200,
    }
}

You will need to install this controller with the following lambda permissions:

• "dynamodb:Query"
• "dynamodb:Scan"
• "dynamodb:GetItem"
• "dynamodb:PutItem"
• "dynamodb:UpdateItem"
• "dynamodb:DeleteItem"
• "dynamodb:DescribeTable"

The OneTable CLI will issue the following commands and set event.action to the method name and event.args to any parameters. The event.config contains the migrate.json settings from the CLI.

function apply(action: String, version: String, params: {dry: boolean}) : Migration {}
function getCurrentVersion() : String {}
function getPastMigrations() {}
function getOutstandingVersions(): String {}

Where a Migration is {version, description, path}.

References

• OneTable.
• OneTable CLI.
• DocumentClient SDK Reference.

Participate

All feedback, contributions and bug reports are very welcome.

• OneTable Migrate Issues

Contact

You can contact me (Michael O'Brien) on Twitter at: @SenseDeepCloud, or email and ready my Blog.

SenseDeep

Please try our Serverless Developer Studio SenseDeep.