Love them or hate the, it’s generally a good idea to apply tags to your AWS resources. We use it primarily for cost allocation tags, but are slowly discovering more usecases.

As your stack grows it can become a chore to remember to apply tags, or even to keep them updated. It can also be a bit annoying to have to keep track of which resources use the Key: Value syntax and which ones use the - Key: key \nValue: value. I was just shown a neat trick by a colleague (shout-out Ilir!) which really highlighted the need to actually read the docs from time to time - SAM parameter file tags, neatly tucked away under Parameter value rules. Unbeknownst to me, this is a configuration file wrapper for the AWS CLI cloudformation create-stack --tags command which applies Stack-level tags to all supported resources in your stack.

Previously to achieve some kind of DRY principle for tagging people would resort to using the Globals section. Don’t do this:

Globals:                # NOT
  Function:             # THE
    Tags:               # BEST
      SomeKey: SomeVal  # WAY

Using Globals has the obvious downside of tags only being applied to the resource AWS::Serverless::Function.

By using the built-in transformation capability of SAM by simply adding tags to your configuration file you can ensure all resources that support tagging will receive it! It’s a super neat way to handle cost allocation tags, versioning, easily searchable strings in the Tag Editor - the possibilities are endless!

# Example samconfig.toml
version = 0.1
[us-east-1]
[us-east-1.deploy]
[us-east-1.deploy.parameters]
stack_name = "api-services"
resolve_s3 = true
s3_prefix = "api-services"
region = "us-east-1"
confirm_changeset = false
capabilities = "CAPABILITY_IAM"
tags = "Product=\"apiServices\" Version=\"0.39\"" # <<-- THIS IS THE MAGIC BIT

Now, without specifying a single tag in the actual template, SAM will ensure that all resources will receive the tags.

Take care of your colleagues and stay open, you never know when they will show you’ve missed.