Unable to connect to RDS during local development with sls offline

Backend
1

I’m facing an issue during local development with sls offline. I’m unable to connect to my RDS instance and keep getting this error: KnexTimeoutError: Timeout acquiring a connection. Has anyone else run into this? Is there a way to work around it or simulate the RDS connection locally so I can continue working with sls offline?

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@Suprith

I faced a similar issue during development and found a way to fix it.

When running sls offline, your Lambda functions attempt to connect to the RDS instance using its AWS-hosted endpoint. However, since this endpoint isn’t accessible from your local machine, the connection fails — resulting in the following error:


KnexTimeoutError: Knex: Timeout acquiring a connection

Use a Local PgAdmin for Offline Development

You can configure your project to connect to a local database while using sls offline, and use the real RDS endpoint when deploying to AWS.

1. Update serverless.yml


environment:

RDS_CLUSTER_HOST: ${env:RDHOST, ssm:RDS_CLUSTER_HOST}

This setup checks:

  • If the RDHOST environment variable is set (used for local development).

  • Falls back to the SSM parameter (RDS_CLUSTER_HOST) in deployed environments.

2. Start Offline with Localhost as Host

Run sls offline like this:


RDHOST=127.0.0.1 sls offline --stage dev --region me-central-1

This tells your Lambda code to connect to a locally running DB (e.g., PostgreSQL or MySQL) instead of the unreachable RDS endpoint.

3. Deploy Normally for AWS Environments

For staging or production, just deploy as usual:


sls deploy --stage prod --region me-central-1

In this case, the real RDS host will be pulled from the SSM parameter store, and your Lambda will work as expected in the AWS environment.

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