# docker
-   daemon must be running (`systemctl start docker`)
-   use `sudo` or add user to group `docker` (`sudo usermod -aG docker user`)
-   [docs](https://docs.docker.com/)
-   there are lots of flavours and tools upon tools, each w/ their own name,
    currently (sept 2018) "docker" usually means "docker ce (community edition)"
-   images are built, containers are running images, aka images w/ command (like class vs instance)
    (not sure if this is correct, but get the idea)

## hello world
```sh
docker version
docker info
docker pull hello-world
docker image ls -a
docker container ls -a
docker run hello-world
docker ps                   # list running container
docker top <container>      # pipes internal top
docker rm <container>
docker rmi <images>
docker rm -f $(docker ps -a -q) # stop and remove all
docker run -it ubuntu bash      # start image
docker exec -it <container> sh  # give interacive shell in running container
docker logs <container>         # show stdout/stderr (?) of running processes
docker system prune -a          # `--all` includes images
```

## dockerfile
-   order sensitive
-   every line is some delta-foo
-   gets images from [hub](https://hub.docker.com/), or local repository
-   minimal image is named "scratch" (`FROM scratch`)
-   minimal userland image is "alpine", which is a minimal linux distro
-   naming convention for images: <version>-<base-system-sometimes-w-version>-<more-stuff>
-   `ENTRYPOINT`: hard-coded command and args to run, sometimes empty,
    overwrite w/ `--entrypoint`
-   `CMD`: default args, overwritten by args passed to `docker run`

file lives in own dir, build w/:

```sh
docker build <dirname>
docker build <dirname> -t <name>:<tag>
docker history <image>
```

## docker compose
configures one or more docker containers and one or more networks.
images are usually referenced by their `name:tag` given on build w/ `-t`.
can handle multiple containers in multiple networks and up/down them all in
one go.

all before `:` is host, all after is in docker.

```sh
docker-compose up
docker-compose down     # all data inside container will be lost
docker-compose pause    # data will be retained, will be resumed on host reboot
docker-compose unpause <id>
docker-compose ps       # like `docker ps`, but with grouping
docker-compose logs
docker-compose run <id> bash    # interactive shell using docker-compose settings
```

## storage
julian says: also check named volumes in
[gitea doc](https://docs.gitea.io/en-us/).

-   volumes: are stored in docker-managed part of fs, e.g.
    `/var/lib/docker/volumes/`, see `docker volume create/ls/prune/...`
-   bind mounts: anywhere on fs, may be modified by anyone at anytime
-   tmpfs mounts

# history / buzzwording
-   kernel namespaces
-   cgroups, `grep "docker\|lxc" /proc/1/cgroup`
-   sdn, software defined network (maybe not `lxc`), can alias names
-   `lxc`, first container implementation by kernel devs
-   `docker`, pimped `lxc`