https://docs.docker.com/storage/volumes/

Update docker container to latest version via docker compose:

#Single container:
docker compose pull calibre-web
docker compose up -d calibre-web
docker image prune

#Update all containers:
docker compose pull
docker compose up -d
docker image prune

Docker compose health checks:
https://medium.com/geekculture/how-to-successfully-implement-a-healthcheck-in-docker-compose-efced60bc08e

Copying files from/to images

docker cp dockerimage:/bla ./bla
docker cp ./bla dockerimage:/bla

Flatten docker image layers:

FROM yourbuildimage as build
# your existing build steps here
FROM scratch
COPY --from=build / /
CMD ["/your/start/script"]

Change mount points of existing docker containers;

e.g. mount /home/<user-name> folder of host to the /mnt folder of the existing (not running) container.

1. stop docker container or whole docker engine

   systemctl stop docker.service

2. Open configuration file corresponding to the stopped container, which can be found at /var/lib/docker/containers/99d…1fb/config.v2.json (may be config.json for older versions of docker). For pretty print use

   vi <(jq . /var/lib/docker/containers/<container-ID>/config.v2.json)
   Save updates to a file: :w config.v2.json
   Exit vim: :q!
   Update existing file: jq -c . config.v2.json > /var/lib/docker/containers/<container-ID>/config.v2.json
    

3. Find MountPoints section: “MountPoints”:{}.
4. Replace the contents with something like this (you can copy proper contents from another container with proper settings):

   "MountPoints":{"/mnt":{"Source":"/home/<user-name>","Destination":"/mnt","RW":true,"Name":"","Driver":"","Type":"bind","Propagation":"rprivate","Spec":{"Type":"bind","Source":"/home/<user-name>","Target":"/mnt"},"SkipMountpointCreation":false}}

   or the same (formatted):

     "MountPoints": {
       "/mnt": {
         "Source": "/home/<user-name>",
         "Destination": "/mnt",
         "RW": true,
         "Name": "",
         "Driver": "",
         "Type": "bind",
         "Propagation": "rprivate",
         "Spec": {
           "Type": "bind",
           "Source": "/home/<user-name>",
           "Target": "/mnt"
         },
         "SkipMountpointCreation": false
       }
     }

5. Start or restart the docker service:

   systemctl start docker.service
   service docker restart

6. Start the container if necessary:

   docker start <container-name/ID>

Containerised PHP & NGINX on Alpine, image size ~60MB:
https://levelup.gitconnected.com/containerizing-nginx-php-fpm-on-alpine-linux-953430ea6dbc
https://github.com/johnathanesanders/docker-nginx-fpm

Log nginx to stdout in Dockerfile:

# forward request and error logs to docker log collector
RUN ln -sf /dev/stdout /var/log/nginx/access.log \
	&& ln -sf /dev/stderr /var/log/nginx/error.log