DevOps Classroomnotes 15/Apr/2023

Docker Volume contd..

Persisting Data using Volumes

• Lets create an explicit volume for mysqldb
• Lets use volume type to mount the mysqldb
• Lets mount a volume using -v Refer Here for official docs
• Create a mysql container

 docker container run -d --name mysqldb -v mysqldb:/var/lib/mysql -P -e MYSQL_ROOT_PASSWORD=rootroot -e MYSQL_DATABASE=employees -e MYSQL_USER=qtdevops -e MYSQL_PASSWORD=rootroot mysql

* Lets create some data

* now delete the container
* Now create a new container using mount

 docker container run -d --name mysqldb --mount "source=mysqldb,target=/var/lib/mysql,type=volume" -P -e MYSQL_ROOT_PASSWORD=rootroot -e MYSQL_DATABASE=employees -e MYSQL_USER=qtdevops -e MYSQL_PASSWORD=rootroot mysql

* As we can see the data is persisted and is attached to new container.

• Lets use bindmount to mount /tmp on docker host to the container /tmp

docker container run -d --name exp1 -v /tmp:/tmp ubuntu:22.04 sleep 1d

docker container run -d --name exp1 --mount "source=/tmp,target=/tmp,type=bind" ubuntu:22.04 sleep 1d

• Login into container and create some data
  
• check the content in /tmp of docker host
  

Creating volume as part of Dockerfile

• Gameoflife:
• Refer Here for the changeset with volume instruction for gameoflife container
  
  

Shell file to clean everything

• Create a shell file with following content

#!/bin/bash
docker container rm -f $(docker container ls -a -q)
docker volume prune
docker image rm -f $(docker image ls -q)

Entrypoint and CMD

• Lets create two docker images
• First

FROM alpine
CMD ["sleep", "1d"]

• Create a container with docker container run first ping -c 4 google.com
  
• Second

FROM alpine
ENTRYPOINT ["sleep"]
CMD ["1d"]

Experiment

• Create a alpine container with the following names

docker container run -d --name C1 alpine sleep 1d
docker container run -d --name C2 alpine sleep 1d

• Now run in C1 ping C2 (docker container exec C1 ping C2)
• Findout ip addresses of C1 container and C2 container by executing

docker container inspect C1
docker container inspect C2

• Now login into C1 and ping C2 by using its ipaddress
• Observation Results
  • ping by name is not working
  • ping by ip is working
    
• Create an ubunutu linux vm
• install net-tools

sudo apt update && sudo apt install net-tools -y
ifconfig

* Now install docker and check network interfaces again ifconfig

* A docker0 network interface is added.

Docker Networks

• Refer Here for the article on docker networking
• Docker has multiple network driver implementations
  • bridge
  • host
  • macvlan
  • overlay
• Bridge:
  • Default bridge will not have dns enabled (this is why in the above experiment C1 was not able to ping C2 by name)
• Create a container C1 in default network docker container run -d --name C1 alpine sleep 1d
• inspect default bridge network docker network inspect bridge
  
• Lets create a new bridge network
  
• Now create two contianers C2 and C3 in my_bridge network
  
• Inspect my_bridge network
  
• Lets try ping from c2 to c3 by name
  
• Lets create a mysql container in my_bridge network

 docker container run -d --name mysqldb -v mysqldb:/var/lib/mysql -P -e MYSQL_ROOT_PASSWORD=rootroot -e MYSQL_DATABASE=employees -e MYSQL_USER=qtdevops -e MYSQL_PASSWORD=rootroot --network my_bridge mysql

• Lets run phpmyadmin

docker container run --name phpmyadmin --network my_bridge -d -e PMA_HOST=mysqldb -P phpmyadmin

* Connect container C1 to my_bridge network

docker container exec C1 ip addr
docker network connect my_bridge C1
docker container exec C1 ip addr
docker network disconnect bridge C1
docker container exec C1 ip addr