Docker

My Docker Notes

Images - images used to create the containers.

Docker file - it is a text(.txt) file with instructions to do the build.

Build - action that creates the image.

Container - instance of the image that presents the execution of the app or service.

Volumes - storage limit. If the containers die, the information in the volumes persists.

Tags - help the image versioning.

Repository - collection of images.

Registry - provides the access of the docker to the repositopry.

Docker Hub

Compose - metadata tool to create multiple containers with only one command.

Intalling docker

sudo apt install docker.io
docker run -it hello-world ## -it = iterative

Commands

run - creates.

ps - list.

info - information.

exec - execute binary from the container

stop/start

logs - shows outputs and logs.

inspect - lists configurations of the container.

pull - download images.

push - share or storage image in the repository.

commit - commit notifications in the containers.

tag - versioning.

login/logout - log on the repository.

search - search image.

rm - remove container.

rmi - remove image.

export/import - export container; merge all layers.

save/load - save/load docker image.

Creating the Container

Add new instance - physical service or Virtual Machine with docker installed.

git clone repository/docker # download the image
docker run --name container hello-world # test installation - create a                                               container
docker run --name container_name -d image_name sleep 3600 # execute during
                                                       # 1 hour
                       #-d demo mode - without output in the screen
docker run --name container_name -d -p 80:80
curl localhost
netstat -nltp # shows opened doors in the server
docker info # summary of what is being executed
docker status
docker ps # shows containers running
docker run --name new_container -p 80:80  -d image_name
#port 80 from server redirecting to port 80 of the container
docker images # list the images

Docker exec

docker exec container mkdir test
docker exec --help
docker exec options <CONTAINER_NAME> <COMMANDS> <ARGUMENTS>
docker exec -it container sh # access the container bash
docker stop container
docker logs container
docker rmi -f image

docker pull image # download the image again without create container to this
docker ps -a
docker commit --author='Author' --message="Image with commit" container_name image
dive container # shows layers - 1st - image; 2nd - folders

Removing

docker ps -a # show all containers including the stopped  or other status
             # ones -a = ALL
docker rmi nginx # RMI to remove images
docker rm -f container_name # -f forced ##RM to remove containers
docker images

Versioning

docker tag container user/image_name:1.0
docker login
docker push user/image_name:1.0 # send your version to dockerhub
docker search image_name
docker run -d --name container user/image_name:1.0 sleep 3600

# Export and import
docker export image_name1 > image_export.tar
cat image_export.tar | docker import -image_export
docker run -d --name image2 image_export sleep 3600

Networks

Bridge - communication between containers. Containers can communite by name. Database in a Virtual Machine and application (flask) in another.

# Create the network
docker network create -d bridge test_bridge
docker network ls

Creates containers and add the network:

docker run -d --net test_bridge --name db netname

Create a container flask front-end:

docker run -d --env "DB=db" --net test_bridge -- name web -p 8000:5000 image
# --env  - environment variable; -p 8000 = server port; 5000 mapping on app port
docker exec -it web sh
#-hostname = container id

Host network.

docker run -d --net host --name db test_bridge # host does not define port
docker run -d --env "DB=db" --net host container_name # creates front-end
netstat # opened ports

Overlay Mode - communication between separated host containers. They need to be inside a cluster. It is necessary to configure a swarm cluster. One of the machines needs to be the manager. The main machine controls the other nodes.

docker swarm init --advertise-addr 192.160.0.18 # it generates an automatic command that must be run in the n servers that will be part of the swarm
docker join --token token_generated
docker node ls

# At the main server
docker network create -d overlay test_overlay

# Creates the back-end
docker service create --network test_overlay --name db image
# Creates front-end
docker service create --network test_overlay -p 8000:5000 -e "DB=db" --name web user/docker_test:1.0 #image
docker network ls
docker ps -a
docker logs # verify connection
netstat

# Scale service - 3 replicates
docker service scale web=3 # number of replicates
docker service ls

Types of Storage

Volume - virtual disk.

Bind Mounts - shared folder between host and container.

tmpfs Mounts - temporary.

Volume

docker volume create my_volume
docker volume ls
docker volume inspect

#Create containers
docker run -d -p 80:80 container -volume --mount source=my_volume.target=/user/share/image/ image:latest

Files that were in the folder you mount, come together. In Bind Mounts it does not happen.

Bind Mounts

# Necessary to create a pre-existent folder
mkdir /html
docker run -d --name container-bind -p 80:80 -v /html/user/share/image/html image # Creates an empty folder, the html file needs to be created

tmpfs

docker run -d --name container_tmpfs --mount type=tmpfs.destination=/cache.tmpfs-size=1000000 image sleep 3600

# Access it
docker exec -it 48 sh

# When it retarts, the cache is erased
# --memory; --cpus = it can be used to limit resources