SSM Design Thoughts

When Jets deploys, it creates Lambda Functions with the Environment Variables from the config/jets/env files. A key point is that Jets resolves the SSM values at deploy time. Here are some thoughts on this SSM design decision.

I’ve considered loading the env values at runtime/bootup time/Lambda cold-start a few times. Ultimately, setting them in the Lambda Function Environment variables is worth the tradeoff. Here are some of the tradeoffs.


  • It’s much easier to debug the environmental variables when you can see what Lambda env variables are used with the AWS Lambda console.
  • There’s no need for IAM permissions at Lambda cold-start time to fetch the SSM value.
  • You won’t have to deal with SSM rate-limiting issues.


  • Lambda Env variables only support simple text to store the values. You can use dynamic resolve:ssm values in CloudFormation, but the values resolve to plain text values. The resolve:ssm-secure is not supported.
  • It’s harder to debug SSM errors like missing names or IAM permissions at cold start times because it happens very early.
  • You have to deal with SSM rate-limiting issues. The jets can handle this with exponential backoff at the cost of some complexity.