While Seed does not need a build spec to configure your pipelines or your project, there are cases where you need to run some scripts during the build process. You can get a sense of the different build steps by looking at one of your build logs.

Build logs screenshot


To hook into the build process, add a seed.yml in the root of your project directory. Here is the basic skeleton of our build spec.

  - echo "Before compile"

  - echo "Before build"

  - echo "Before deploy"

  - echo "After deploy"

  - echo "Before deploy"

  - echo "After deploy"

Below is a brief description of when these commands are run.

  • before_compile

    Seed starts the build process by doing a npm install (for Node.js projects), pip install -r requirements.txt (for Python projects), or make (for Go projects). The before_compile step let’s you run commands before this. This can be useful for configuring private npm modules.

  • before_build

    The actual build portion for Seed is the serverless package command that creates the build. The before_build step let’s you run your commands before this happens.

  • before_deploy

    After the build packages are created, Seed deploys these using the serverless deploy command. The before_deploy let’s you run your commands before this happens. This step is run for all services and also when they are promoted to production. You can distinguish between the cases by using the $SEED_STAGE_NAME build environment variable.

  • after_deploy

    After the deployment is complete you can use the after_deploy step to run any post deployment scripts you might have. Again, this step is run for all services and also when they are promoted to production. You can distinguish between the cases by using the $SEED_STAGE_NAME build environment variable.

    Note that for SST apps, Seed uses an integrated deployment process (to make your CDK deployments free). So any script executed after the deployment, is run in a separate build process. It’ll also automatically restore the node_modules/ cache before running your scripts.

  • before_remove

    Seed runs the serverless remove command to remove a deployed service. The before_remove step let’s you run any commands before this happens. Note that, this step is only run when a service is being removed.

  • after_remove

    Similar to the before_remove, the after_remove step is run after a service has been removed. This can be used to run any cleanup scripts you might have.

Other Options

Apart from the build hooks, there are a couple of other options that can help you customize the Seed build process.

Checking code changes

Seed by default checks the Git log to see if a service has been updated, before deploying it. You can read more about this in our Deploying Monorepo Apps chapter.

Add the following to either, disable this check:

check_code_change: false

Or use the Lerna algorithm instead:

check_code_change: lerna

Customize stage names

The stage name is central to the way Seed manages deployments and resources for your Serverless app. It is either specified manually or Seed automatically generates it based on the auto-deployed branch. If it’s being generated, Seed will sanitize the branch names so it works with Serverless Framework and AWS.

However, there might be rare cases where you might wish to customize the automatically generated stage names. To do so, specify a bash command using the stage_name_constructor option. Note that:

  • This only applies to auto-deployed branches.
  • It’s only run the first time, while creating the stage.
  • The command needs to print out a string to stdout.
  • It has access to the $SEED_STAGE_BRANCH environment variable.
  • There’s a timeout of 2 seconds for the command.
  • If the commands fails or times out, Seed will use the automatically generated stage name.

Let’s look at an example. Say your feature branches have the naming convention feature/feature-name. However, you want the stage names to be feature-name. And you don’t want to transform some specific branch names. Add the following to your seed.yml.

stage_name_constructor: >
  if [ $SEED_STAGE_BRANCH = 'master' ]; then
    echo 'master'
  elif [ $SEED_STAGE_BRANCH = 'beta' ]; then
    echo 'beta'
    echo $SEED_STAGE_BRANCH | cut -d'/' -f2

Build Environment Variables

Seed also has a couple of build environment variables that you can use to customize your build process. These should not be confused with the secret environment variables that are defined in the console.

  • $SEED_STAGE_NAME: The name of the stage that is being built. The stage names are exactly as shown in the console.
  • $SEED_STAGE_BRANCH: The name of the git branch the stage is auto-deployed from. If the stage is not auto-deployed, the value is not defined.
  • $SEED_APP_NAME: The app name.
  • $SEED_SERVICE_NAME: The name of the service.
  • $SEED_BUILD_ID: The build id.
  • $SEED_BUILD_SERVICE_SHA: The commit SHA used to build a given service. For post-deploy phases, if the build is using multiple commits, the first commit will be set. If the service is being removed, it is set to the commit used in the last successfully deployed build.
  • $SEED_BRANCH: The Git branch used to trigger this build. Does not apply to promotions and rollbacks. For PR stages, this is the branch the PR was submitted to. Note the difference between this and the $SEED_STAGE_BRANCH variable. These two variables will differ if you trigger a manual deployment using a branch that’s different from the one the stage is set to auto-deploy from.
  • $SEED_PULL_REQUEST_NUMBER: For PR stages, this is the number of the Pull Request.

  • Secrets: All your secrets in the Seed console are also made available during the build process. For example, a secret environment variable called TEST_VAR would be available as $TEST_VAR in the build process.

For example, let’s take a build URL in the console:


Here the $SEED_APP_NAME would be serverless-app, $SEED_STAGE_NAME would be dev, $SEED_SERVICE_NAME would be users, and $SEED_BUILD_ID would be 32.

Custom Build Environment Variables

Environment variables that are set in the build spec do not persist across commands. This means that in the following build spec, $MY_VAR will not be printed out.

  - export MY_VAR=hello
  - echo $MY_VAR

To ensure that your custom build environment variables persist across commands; Seed allows you to do something similar to CircleCI. You export your custom environment variables to a $BASH_ENV and Seed will load that on every command.

So a variation of the above with $BASH_ENV looks like this:

  - echo 'export MY_VAR=hello' >> $BASH_ENV
  - echo $MY_VAR

In this case $MY_VAR is loaded from $BASH_ENV and should be printed out correctly.


The scripts in your build spec are run in an environment that are using your AWS IAM credentials. This means that you can directly use any AWS commands in your script using the AWS CLI without having to configure it.

Build Spec Examples

Here are a couple of examples of what you could do in a build spec.

Run a script after deploy only in prod

Let’s assume your production stage is called prod.

  - if [ $SEED_STAGE_NAME = "prod" ]; then echo 'deployed prod'; fi

Run a script after deploying a specific service

Let’s assume your service is called users.

  - if [ $SEED_SERVICE_NAME = "users" ]; then echo 'deployed users'; fi

And if you wanted to combine two conditions you can do:

  - if [ $SEED_STAGE_NAME = "prod" ] && [ $SEED_SERVICE_NAME != "users" ]; then echo 'deployed users to prod'; fi

Install PostgreSQL

If you need to start a PostgreSQL server locally for tests.

  - apt-get install wget ca-certificates -y
  - wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | apt-key add -
  - sh -c 'echo "deb http://apt.postgresql.org/pub/repos/apt/ `lsb_release -cs`-pgdg main" >> /etc/apt/sources.list.d/pgdg.list'
  - apt-get update
  - apt-get install postgresql postgresql-contrib -y

Invoke a Lambda Function

If you want to invoke a Lambda function as a part of your build process.

  - >
    aws lambda invoke
    --function-name my-function
    --payload '{"name":"Bob"}'

This works because the AWS CLI is available and configured with the IAM credentials of the stage.

Reference CloudFormation output

If you want to use a CloudFormation output from a different stack use the following.

  - echo "export MY_KEY=$(aws cloudformation describe-stacks --stack-name my-stack --query 'Stacks[0].Outputs[?OutputKey==`MY_KEY`].OutputValue | [0]' --output text)" >> $BASH_ENV
  - echo $MY_KEY

This’ll use the AWS CLI to get the information of my-stack; parse the output for the value of OutputKey MY_KEY; and then export the value as the $MY_KEY environment variable. Then you’ll be able to reference this value in your serverless.yml as ${env:MY_KEY}.

If you are trying to get the outputs for a stack that’s in a different region than the currently deployed stage, use the --region option in the AWS CLI.

Running Docker commands

You’ll need to enable Docker to use it in your build spec. Head over to our chapter on running Docker commands for further details.