A very common need is to quickly identify what version of the software a Docker image is running and optionally stick to it, or to be sure to always run a stable version. This is a perfect use for the Docker tags. We'll build a Terraform container, with both a stable and an unstable tag, so multiple versions can coexist—one for production and one for testing.
Note
Docker tags are not to be mistaken with Docker labels. Labels are purely informative when tags can be requested directly to make images distinct from an operational point of view.
Here's a simple Dockerfile to create a Terraform container (Terraform was covered earlier in this book):
FROM alpine:latest
ENV TERRAFORM_VERSION=0.7.12
VOLUME ["/data"]
WORKDIR /data
RUN apk --update --no-cache add ca-certificates openssl && \
wget -O terraform.zip "https://releases.hashicorp.com/terraform/${TERRAFORM_VERSION...