Emulating Kubernetes volumeMount, emptyDir, env and envFrom during local Docker dev lifecycle

When deploying a container to Kubernetes, you can mount files and secrets to specific locations in the filesystem, as well as populate environment variables from a file or key.

For example, with an NGINX container you can mount:

• /etc/nginx/nginx.conf - control the NGINX configuration
• /usr/share/nginx/html/index.html - the default content delivered
• /var/log/nginx - as an ephemeral directory for logs

or set environment variables:

• env.properties - use a file to set an entire list of key/value pairs
• set a single key/value

But how do you emulate these when you are going through the software development lifecycle using a local Docker service?

These volume and environmental values can also be set using a Docker swarm file, but that is not a focus of this example.

Docker file mounting using volume

You can mount local files to a specific location using the '-v' volume flag. For example:

docker ... -v /my/local/path/nginx.conf:/etc/nginx/nginx.conf:ro

Docker ephemeral directories using tempfs

You can create ephemeral directories using a tmpfs mount. For example:

docker ... --mount type=tmpfs,destination=/var/log/nginx

We are using '--mount' instead of the '--tmpfs' flag for interoperability with OS other than Linux.

Docker single environment variable

docker ... --env key=value

Docker set environment variables from file

docker ... --env-file env.properties

Test Kubernetes volume mounts and env vars

sudo apt install git curl make -y
make k8s-apply
make k8s-test

Test equivalent Docker volume mounts and env vars

sudo apt install git curl make -y
make
make docker-run-bg
make test