Thread by @FrancescoCiull4

THE 🐳IS BACK !!! 🧵🧵🧵

During these days, even if you have seen not that much from the social point of view, I have continued working on Docker and I am thinking about something you could enjoy in the future!

In the meanwhile, here is a Thread of useful Docker Tips

👇👇👇

DOCKER DESKTOP

Dockerfile keywords

DOCKER EXEC

Execute commands on currently running containers.

The most popular usage is to launch a Terminal in a running container, keeping the STDIN open and allocating a pseudo-TTY.

Example:
"docker exec -it <cont_ID> /bin/bash"

HEALTHCHECK in Dockerfiles

Healthchecks are what they sound like: a way to check if the container is 'healthy'. You can specify an healthcheck to check if a container is running properly.

They are very important in a real-world scenario and production-ready applications

DOCKER COMPOSE
Multiple compose files:

By default, Compose reads 2 files:
- docker-compose.yml (base config)
- docker-compose.override.yml file (to override config)

If a service is defined in both files, configurations are merged, useful for development

Docker-compose commands

docker stats [OPTIONS] [CONTAINER...]
returns a live data stream for containers.

Below a custom command, using GO template, that shows additional info you can try.

docker stats -a --format "table {{.ID}}\t{{.Name}}\t{{.CPUPerc}}\t{{.MemUsage}}\t{{.MemPerc}}\t{{.BlockIO}}"

DELETE ALL NOT RUNNING CONTAINERS

CHECK ENVIRONMENT VARIABLES OF AN IMAGE

DOCKER TOP: Displays the container's running processes
DOCKER PORT: Lists container's port mappings
DOCKER KILL: Kills the process! (not ideal)

DOCKER DIFF
An handy command to check any changes to:
-files
-directories

on the container’s filesystem

A: added file or directory
C: changed file or directory was
D: deleted file or directory

Usage:
docker diff <container_ID/container_name>

docker container ps [OPTIONS]
(you can use the shortcut: "docker ps [OPTIONS]")

-a: show all containers, even the stopped ones
-q: only show IDS
-l: show the latest container
-s: show the size
-f: filter output
--format: show using GO template (example below)

DOCKER TAG:
docker tag <image> <new tag>

Effect:
Create a tag image that refers to the source image

A tag must be:
- valid ASCII
- may contain letters, digits, underscores, periods, dashes.
- may not start with a period or a dash
- maximum of 128 characters.

DOCKER VOLUMES:
The preferred mechanism for persisting data for Docker containers

- Special directory for containers
- Designed to persist data
- No automatically deleted
- No garbage-collected when no more referenced

Types:

-HOST VOLUMES
-NAMED VOLUMES
-ANONYMOUS VOLUMES

DOCKER UN OPTIONS:

-d: detached mode
-e: set/override env variable
-i: Keep STDIN open
--name: assign name
--network: define network
-p: publish ports
-P: publish all the ports to the host interfaces
--rm: remove on exit
-t: pseudo-tty
-u: user
-v: volume
-w: default workdir

Containers pro over VMs:

1⃣Dev-Friendly

2⃣Smaller Snapshots (Images)

3⃣Public Registry (Docker Hub)

4⃣Faster startup (seconds, no minutes)

5⃣Less Resource-Consuming (Processes)

6⃣The App runs independently on computer/OS

7⃣New containers can be created on-demand quickly

.dockerignore file

DOCKER PRUNE COMMANDS

DOCKER STOP / DOCKER RM deep dive

What happens when we use these commands?

How can we send a SIGNAL to a container?

Docker Volume PRO over Bind-Mount:

1⃣Easier back up/migration
2⃣Manageable by Docker CLI/API
3⃣Work on Linux/Windows containers
4⃣Shared safer among containers
5⃣Storable on remote hosts/cloud providers to encrypt contents/add functionalities
6⃣Can have content pre-populated

DOCKER NAMESPACES

Docker is written in Go and takes advantage of several features of the Linux kernel to deliver its functionality.

One of these is 'Namespaces':

The Docker Engine combines
- namespaces
- cgroups
- UnionFS

To define a container format.

Current: libcontainer

DOCKER CMD & ENTRYPOINT

DOCKERFILE GO EXAMPLE

DOCKER MINIMALISTIC DEFINITIONS (Thread)

https://twitter.com/FrancescoCiull4/status/1318150257306443778