Docker Cheatsheet

Table of content

1. Install
2. First Containers
3. container commands
4. images commands
5. Dockerfile
6. Links

1. Install

1.1 CentOS 7.x installation

link

install

sudo yum install -y yum-utils device-mapper-persistent-data lvm2
sudo yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
sudo yum install docker-ce docker-ce-cli containerd.io
sudo systemctl enable docker
sudo systemctl start docker

verify

sudo systemctl status docker
sudo docker info
sudo docker run hello-world

1.2 CentOS 7.6 with Vagrant/Virtualbox

cd centos-configured
vagrant up
vagrant ssh

1.3 Ubuntu 18.04 installation

link

install

sudo apt-get update
sudo apt-get install apt-transport-https ca-certificates curl gnupg-agent software-properties-common
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
sudo apt-get update
sudo apt-get install docker-ce docker-ce-cli containerd.io

verify

sudo systemctl status docker
sudo docker info
sudo docker run hello-world

2. First Containers

hello-world

docker run hello-world

centos

docker run -it centos
cat /etc/centos-release
du -sh / 2>/dev/null

ubuntu

docker run -it ubuntu
cat /etc/debian_version
cat /etc/issue
du -sh / 2>/dev/null

alpine

docker run -it alpine
cat /etc/alpine-release
cat /etc/issue
du -sh / 2>/dev/null

busybox

docker run -it busybox
du -sh /

3. Containers commands

3.1 List

# show running containers
docker ps
# show last container
docker ps -l
# show all containers ( including stopped )
docker ps -a
# show container sizes
docker ps -s

full container ID

[root@desktop-08ut1lq ~]# docker ps -lq --no-trunc
cb9defb0841671a779f1527e5e30aa6c8b03d9bad9a42e61875368a9de6ae5f7
[root@desktop-08ut1lq ~]# docker ps -l
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS                      PORTS               NAMES
cb9defb08416        busybox             "sh"                11 minutes ago      Exited (0) 11 minutes ago                       gracious_villani

3.2 Run

# run in interactive mode
docker run -it ubuntu
# run in background
docker run -d httpd
# detach: Ctrl^P, Ctrl^Q
# attach <cid>
docker attach fe8
# run interactive in background
docker run -itd ubuntu
# check running
docker ps

3.3 Stop

# try gracefully stop container (SIGTERM, 10s wait)
docker stop <cid>
# just kill
docker kill <cid>

3.4 Read Logs

# show logs
docker logs <cid>
# show last 5 lines
docker logs --tail 5 <cid>
# tail -f
docker logs --tail 5 --follow <cid>

httpd example

docker run -d -P httpd
docker port $(docker ps -lq)
-> 80/tcp -> 0.0.0.0:32768
# on another console generate load
while sleep 1; do curl localhost:32768; done
# on main console
docker logs --tail 1 --follow $(docker ps -lq)

3.5 Exec

# exec something in running container
docker exec -it <cid> '/bin/bash'

4. Images commands

# list
docker images
# download
docker pull
# delete
docker rm

5. Dockerfile

5.1 nslookup

v1

# create environment
cd /vagrant
touch Dockerfile
# edit ...

cat Dockerfile

FROM centos
RUN yum install -y bind-utils

build

# docker build -t tag, nslookup - image name
docker build -t nslookup .

v2

FROM centos
RUN yum install -y bind-utils
ENTRYPOINT ["nslookup"]
CMD ["google.com"]

5.2 Dockerfile basic instructions

FROM - define which container loaded on current step. Used to define starting build point

FROM centos

RUN - define command which run in container in current step. Used to record actions in container

RUN yum clean && yum update metadata && yum update
RUN wget https://artifactory.intranet/generic-windows/app.msi

ENTRYPOINT - define command that run during container starting CMD - does the same. ENTRYPOINT vs CMD diff: ENTRYPOINT not overrided during container run

ENTRYPOINT ["echo"]
CMD ["hello"]

COPY - copy files into docker containers, from context and other containers

COPY /app /opt

FROM ubuntu as 'builder'
RUN ...
...
COPY --from /opt/hello/hello /bin/hello

ENV - set container environment variable

FROM ubuntu
ENV PG_MAJOR 9.3
ENV PG_VERSION 9.3.4
...

EXPOSE - expose container networking ports

EXPOSE 80
EXPOSE 80/tcp
EXPOSE 80/udp

5.3 flask-hello example

https://pythonspot.com/flask-hello-world/

from flask import Flask
app = Flask(__name__)

@app.route("/")
def hello():
    return "Hello World!"

if __name__ == "__main__":
    app.run()

commands:

docker run -it centos
# centos
yum install -y epel-release
yum install -y pip
pip install flask

5.4 multistage example

int main () {
  puts("Hello, world!");
  return 0;
}

commands:

yum install gcc make
make hello

6 Docker volumes

docker volume create app_config
docker volume rm app_config
docker volume ls
docker volume inspect

# docker volume create app_config
# docker run -d -P -v app_config:/opt/config nginx

# mkdir /opt/nginx_config
# docker run -d -P -v /opt/nginx_config:/opt/config nginx

100. Links

https://container.training/ - BiS

** https://github.com/wsargent/docker-cheat-sheet - comprehensive cheat-sheet**

https://docs.docker.com/ - official documentation

ENTRYPOINT vs CMD: https://goinbigdata.com/docker-run-vs-cmd-vs-entrypoint/