# docker

• Wercker: You have reached your pull rate limit.

  Have you seen this error on Wercker:

  You have reached your pull rate limit. You may increase the limit by authenticating and upgrading: https://www.docker.com/increase-rate-limit"

  If you are an occassional/hobby builder then a free account on Docker Hub is all you will need to resolve the issue. Read on for a step-by-step guide.

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• Docker Compose Default Environment Variables

  Use ${VAR:-VALUE} to specify VALUE as the default value if $VAR is not set or is empty.