Docker

get in to a Docker

docker exec -it [mycontainer or ID] sh

Dockerfile Basic Syntax

```Dockerfile
# Base image to build layer on top
FROM node:18-alpine

# Working directory for build and runtime
WORKDIR /app

# Copy from "build context" into container image
COPY . .

# Run command during build time
RUN npm install

# Instructions what to run when container starts
CMD ["node", "src/index.js"]

[Additional Dockerfile instructions https://docs.docker.com/reference/dockerfile/]

ENV           - Variables available to RUN commands and on container execution.
ARG           - Arguments you can pass to `docker build` to customize an image.

RUN \
  --mount     - Mount a volume during build.
  --network   - To deactivate the network for this step or to use the host network. 
  --security  - Similar to `docker run --priviliged` for build time.

USER          - User and group ID used for the following RUN, CMD and/or ENTRYPOINT.
SHELL         - Override default shell for RUN, CMD and ENTRYPOINT (e.g. powershell instead of cmd in Windows Containers).

EXPOSE        - "Documentation" about which ports should be exposed (no actual effect).
VOLUME        - Creates volumes on `docker run` ("ignored" by Kubernetes).

ONBUILD       - Sneak in Dockerfile instructions if image is used as base image (scary magical feature).
STOPSIGNAL    - Signal to stop container ie. SIGKILL, SIGTERM...
HEALTHCHECK   - Docker specific feature for health checks (ignored by Kubernetes).

LABEL         - Metadata key value pairs: org.opencontainers.image.authors="hans@letsboot.ch"
MAINTAINER    - Sets the Author field of the generated images (deprecated)