drift

dynamo-drift

dynamo-drift is a minimalistic library for performing DynamoDB schema migrations.

Individual migrations are code that is executed in the context of a callback performed per existing table item. You can execute actions within callbacks (update/insert/delete) which are deferred until after all callbacks complete, or use the DynamoDB client directly for immediate table operations. Migrations and actions can modify any table, not just the target table of the migration (this allows a migration from one table into another, for example).

dynamo-drift:

• keeps track of migrations already executed via a separate configurable metadata table
• executes the supplied migrations, each with the requested concurrency
• queues and executes actions (insert/update/delete) after callbacks finish so that they do not interfere with the main table scan

It is the responsibility of the application to determine:

• what a migration consists of and when it may be executed
• when to rollback or undo a migration, and what that means
• how many active migrations exist at any given time

Example

import (
  "github.com/aws/aws-sdk-go/aws/session"
  "github.com/aws/aws-sdk-go/service/dynamodb"
  "github.com/dollarshaveclub/dynamo-drift"
)

func main() {
  // get authenticated DynamoDB client
  client := dynamodb.New(session.Must(session.NewSession()))

  // create migrator
  dd := drift.DynamoDrifter{}
  dd.MetaTableName = "MyMigrationsTable"
  dd.DynamoDB = client

  // initialize
  dd.Init(10, 10)

  // check applied
  migrations, _ := dd.Applied()
  fmt.Printf("migrations already applied: %v\n", len(migrations)) // "migrations already applied: 0"

  // create migration
  migration := &drift.DynamoDrifterMigration{
    Number: 0,
    TableName: "MyApplicationTable",
    Description: "readme test",
    Callback: migrateUp,
  }

  // run migration
  errs := dd.Run(context.TODO(), migration, 1, true)
  for _, err := range errs {
    fmt.Printf("error during up migration: %v", err)
  }

  migrations, _ = dd.Applied()
  fmt.Printf("migrations already applied: %v\n", len(migrations)) // "migrations already applied: 1"

  migration.Callback = migrateDown

  // run undo migration
  errs := dd.Undo(context.TODO(), migration, 1, true)
  for _, err := range errs {
    fmt.Printf("error during down migration: %v", err)
  }

  migrations, _ = dd.Applied()
  fmt.Printf("migrations already applied: %v\n", len(migrations)) // "migrations already applied: 0"
}

// Callbacks are executed once for each item in the target table
func migrateUp(item drift.RawDynamoItem, action *drift.DrifterAction) {
  // modify this table item somehow
}

func migrateDown(item drift.RawDynamoItem, action *drift.DrifterAction) {
  // do something to undo migration
}