parameter-store-exec

Run a program with AWS Systems Manager Parameter Store parameters injected as environment variables. Perfect for a Docker ENTRYPOINT to load secret and plain configuration in production AWS.

A parameter store path is read from the PARAMETER_STORE_EXEC_PATH environment variable, which is easy to inject at runtime with docker run --env .... All parameters stored under that path are loaded into environment, with their keys converted to ENV_FRIENDLY names. For path /one/two the key /one/two/three/four becomes THREE_FOUR.

# which AWS region to use; sometimes pre-set e.g. under `aws-vault`.
export AWS_REGION=us-east-1

# Parameter Store path to load into environment.
export PARAMETER_STORE_EXEC_PATH=/foo/bar

# Simle command; just put `parameter-store-exec` in front of your command:
parameter-store-exec <command [args ...]>

Prior art

cultureamp/s3dotenv is a similar tool, but backs onto an S3 bucket containing a dotenv file. It may still be useful, but Parameter Store is more suitable for storing production runtime configuration, with per-key encryption, versioning and audit.

segment/chamber is a larger and more opinionated way to manage Parameter Store configuration. It's more restrictive regarding hierarchical path namespacing, a feature added to Parameter Store after chamber was first written. It also needs a service name (parameter namespace) provided on the command line for chamber exec, making it harder to parameterize via environment at runtime. Segment did an excellent write-up on using Parameter Store for secure configuration on AWS, and particularly ECS.

Droplr/aws-env also backs onto Parameter Store, but only outputs env vars ready for shell eval, making it less suitable (but workable) as a Dockerfile ENTRYPOINT.

Demo

Store some parameters:

aws ssm put-parameter --name /acme/staging/hello --value world --type String
aws ssm put-parameter --name /acme/staging/xyz/username --value acme-staging --type String
aws ssm put-parameter --name /acme/staging/xyz/password --value hunter2 --type SecureString

Run a command with environment injected from Parameter Store:

export AWS_REGION=us-east-1
export PARAMETER_STORE_EXEC_PATH=/acme/staging

parameter-store-exec env
# (stderr) 2017/12/06 15:18:12 /acme/staging/hello => HELLO
# (stderr) 2017/12/06 15:18:12 /acme/staging/xyz/username => XYZ_USERNAME
# (stderr) 2017/12/06 15:18:12 /acme/staging/xyz/password => XYZ_PASSWORD
# ...
# HELLO=world
# XYZ_USERNAME=acme-staging
# XYZ_PASSWORD=hunter2
# ...

Those log messages are on stderr; easy to hide:

parameter-store-exec env 2>/dev/null
# ...
# HELLO=world
# XYZ_USERNAME=acme-staging
# XYZ_PASSWORD=hunter2
# ...

In a Dockerfile:

ENTRYPOINT ["parameter-store-exec"]

Then you can inject the desired Parameter Store path at runtime:

docker run --env PARAMETER_STORE_EXEC_PATH=/acme/staging $image env
# (stderr) 2017/12/06 15:18:12 /acme/staging/hello => HELLO
# (stderr) 2017/12/06 15:18:12 /acme/staging/xyz/username => XYZ_USERNAME
# (stderr) 2017/12/06 15:18:12 /acme/staging/xyz/password => XYZ_PASSWORD
# ...
# HELLO=world
# XYZ_USERNAME=acme-staging
# XYZ_PASSWORD=hunter2
# ...

Or use that same Docker image in a non-AWS environment; just don't pass PARAMETER_STORE_EXEC_PATH:

docker run --env HELLO=local $image env
# (stderr) 2017/12/06 15:21:45 PARAMETER_STORE_EXEC_PATH not set
# HELLO=local