Dynamodb: add GSI to existing Dynamodb table via CDK deploy

[mattiLeBlanc]

A way to use Table.addGlobalSecondaryIndex for existing tables so we can Add an inde to a existing table using the CDK.

Use Case

I create my DynamoDB tables via the CDK.

Now I have to add an index, so I want to ideally update the existing table and not recreate the table (no delete policy is enabled).
So, in my CDK script I check (using the SDK) if the table already exists. If it doesn't exist I use :

const table = new Table(this, tableName, options);
// and 
table.addGlobalSecondaryIndex(options);

to create table and GSI.

However, if the table does already exist (in staging or prod), I am using

const table = Table.fromTableName(this, tableName, tableName);

to get a table reference ( so I can use that to get the datasource for Appsync resolvers and such).

The problem I have is that fromTableName returns an interface of ITable and not Table. ITable doesn't have the addGlobalSecondaryIndex function, only Table does.
So there is no way for me (as far as I know) to add an index to an existing table, either then removing the table first (bad) or adding it manually.

I have add a hacky workaround in my CDK deploy script using the SDK where I use the updateTable command from @aws-sdk/client-dynamodb however that is not ideal.

Proposed Solution

If the Table.fromTableName function would return a Table interface, that could allow us to call addGlobalSecondaryIndex or removeGlobalSecondaryIndex and update our tables via the CDK.

Other

• 👋 I may be able to implement this feature request
• ⚠️ This feature might incur a breaking change

---

This is a 🚀 Feature Request

[skinny85]

That's not something we can accommodate @mattiLeBlanc . We can't modify resources in the CDK that are not managed in the CDK.

If you want to do different things in test / prod, you need to vary it in code:

const app = new cdk.App();

// test
new MyStack(app, 'TestStack');

// prod
new MyStack(app, 'ProdStack', {
  table: 'my-table-arn',
});

interface MyStackProps extends cdk.StackProps {
  readonly table?: string;
}

class MyStack extends cdk.Stack {
  readonly table: dynamodb.ITable;

  constructor(scope: Construct, id: string, props?: MyStackProps) {
    super(scope, id, props);

    if (props.table) {
      this.table = dynamodb.Table.fromTableArn(this, 'Table', props.table);
    } else {
      this.table = new dynamodb.Table(this, 'Table', {
        // do whatever you need here...
      });
    }
  }
}

Thanks,
Adam

[mattiLeBlanc]

@skinny85
Hi Adam,

I am using a stack to create my table, it is just when I want to update a deployed table by adding an index, I want to do it through the CDK and not manually for each env and developer that might have the stack deployed.

fromTableArn and fromTableName both return an ITable interface which doesn't allow me to add a GSI (it doesn't implement addGlobalSecondaryIndex().
Does this mean that adding a new GSI or changing an existing can only be done via the SDK and not the CDK?

[skinny85]

Does this mean that adding a new GSI or changing an existing can only be done via the SDK and not the CDK?

Yes. If you want a GSI added to a Table using the CDK, that Table also needs to be created by the CDK.

[skinny85]

Generally, those things are done in CDK by code changes. You change the code to add the GSI to your CDK-managed Table, and then everyone who updates their code will get the GSI the next time they deploy their Stacks.

[mattiLeBlanc]

@skinny85 I think we are misunderstanding each other. My table is created by CDK. The problem is that in the docs or typescript definition I do not see a way to add a GSI to an existing table.
the addGlobalSecondaryIndex is only available on the table object returned by the const table = new Table(this, tableName, options); constructor, which returns an interface of Table.

When I already have a table with production data and I we decide to add an index later, I can't remove the table and recreate because I don't want to lose data.

Using the fromTableArn or fromTableName is not returning a Table object but and interface of ITable which doesn't seem to have a function to add or update an index.

Do you understand my issue now?