Dockerfiles

Creating portable images

Dockerfile defines what goes on in the environment inside your container. Access to resources like networking interfaces and disk drives is virtualized inside this environment, which is isolated from the rest of your system, so you need to map ports to the outside world, and be specific about what files you want to "copy in" to that environment. However, after doing that, you can expect that the build of your app defined in thisDockerfilebehaves exactly the same wherever it runs.

Docker build command

docker build -t friendlyhello .

Best Practices for writing Dockerfiles

1. Create ephemeral containers
2. Understand build context
3. Pipe Dockerfile through stdin
4. Exclude with .dockerignore
5. Use multi-stage builds
6. Don't install unnecessary packages
7. Decouple applications
8. Minimize the number of layers
9. Sort multi-line arguments
10. Leverage build cache

Dockerfile instructions

1. FROM FROM python:3.7.2-slim

2. LABEL

3. RUN

   • APT-GET
   • USING PIPES

4. CMD

   CMD [ "python", "logger.py" ]

5. EXPOSE

6. ARG

   The ARG instruction defines a variable that users can pass at build-time to the builder with the docker build command using the --build-arg <varname>=<value> flag.

7. ENV

8. ADD or COPY

   ADD logger.py logger.py

   COPY takes in asrcanddestination. It only lets you copy in a local file or directory from your host (the machine building the Docker image) into the Docker image itself

   ADD lets you do that too, but it also supports 2 other sources. First, you can use a URL instead of a local file / directory. Secondly, you can extract a tar file from the source directly into the destination

9. ENTRYPOINT

10. VOLUME

11. USER

12. WORKDIR

13. ONBUILD

• RUN executes command(s) in a new layer and creates a new image. E.g., it is often used for installing software packages.

• CMD sets default command and/or parameters, which can be overwritten from command line when docker container runs.

• ENTRYPOINT configures a container that will run as an executable.

• Shell & Exec form

http://goinbigdata.com/docker-run-vs-cmd-vs-entrypoint

https://docs.docker.com/develop/develop-images/dockerfile_best-practices

https://www.docker.com/blog/intro-guide-to-dockerfile-best-practices

Advanced

https://www.docker.com/blog/advanced-dockerfiles-faster-builds-and-smaller-images-using-buildkit-and-multistage-builds

https://sysdig.com/blog/dockerfile-best-practices

Building Small Containers (Kubernetes Best Practices)