What is Docker?
Docker is an open-source platform that automates the deployment, scaling, and management of applications using containerization. It allows you to package an application with all its dependencies into a standardized unit for software development and deployment.
Key Concepts:
1. Containers
- Lightweight, standalone executable packages
- Include everything needed to run an application
- Ensure consistency across different environments
2. Images
- Read-only templates used to create containers
- Built from layers, each representing an instruction in the Dockerfile
- Can be shared via Docker Hub or private registries
3. Dockerfile
- Text file containing instructions to build a Docker image
- Defines the environment inside the container
- Automates the image creation process
4. Docker Compose
- Tool for defining and running multi-container Docker applications
- Uses YAML files to configure application services
- Simplifies complex setups with a single command
5. Docker Swarm
- Native clustering and scheduling tool for Docker
- Turns a pool of Docker hosts into a single, virtual host
- Enables easy scaling and management of containerized applications
Benefits of Docker:
• Consistency: "It works on my machine" becomes a thing of the past
• Isolation: Applications and their dependencies are separated from the host system
• Efficiency: Lightweight containers share the host OS kernel, reducing overhead
• Portability: Containers can run anywhere Docker is installed
• Scalability: Easy to scale applications horizontally by spinning up new containers
Best Practices:
1. Keep images small and focused
2. Use multi-stage builds to optimize Dockerfiles
3. Leverage Docker Compose for local development
4. Implement proper logging and monitoring
5. Regularly update base images and dependencies
6. Use volume mounts for persistent data
7. Implement proper security measures (e.g., least privilege principle)
Getting Started:
1. Install Docker on your machine
2. Familiarize yourself with basic commands (docker run, build, pull, push)
3. Create your first Dockerfile and build an image
4. Experiment with Docker Compose for multi-container setups
5. Explore Docker Hub for pre-built images and inspiration
Docker has become an essential skill for developers and operations teams alike.
Its ability to streamline development workflows, improve deployment consistency, and enhance scalability makes it a crucial tool in modern software development.
𝗜𝗺𝗮𝗴𝗲 𝗠𝗮𝗻𝗮𝗴𝗲𝗺𝗲𝗻𝘁
- Use 𝚍𝚘𝚌𝚔𝚎𝚛 𝚋𝚞𝚒𝚕𝚍 to create images from Dockerfiles, the blueprint for containers.
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚙𝚞𝚕𝚕 to download pre-built images from registries like Docker Hub.
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚙𝚞𝚜𝚑 to upload your images to remote registries.
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚒𝚖𝚊𝚐𝚎𝚜 lists locally stored images.
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚛𝚖𝚒 removes unwanted images.
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚝𝚊𝚐 tags images for organizational purposes.
𝗖𝗼𝗻𝘁𝗮𝗶𝗻𝗲𝗿 𝗟𝗶𝗳𝗲𝗰𝘆𝗰𝗹𝗲
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚛𝚞𝚗 launches a container from an image.
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚜𝚝𝚘𝚙 and 𝚍𝚘𝚌𝚔𝚎𝚛 𝚔𝚒𝚕𝚕 halt running containers gracefully or forcibly.
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚛𝚎𝚜𝚝𝚊𝚛𝚝 restarts a stopped container.
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚛𝚎𝚗𝚊𝚖𝚎 to rename existing containers.
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚕𝚘𝚐𝚜 prints logs of a container.
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚎𝚡𝚎𝚌 runs commands interactively in a container.
𝗡𝗲𝘁𝘄𝗼𝗿𝗸𝗶𝗻𝗴 𝗮𝗻𝗱 𝗦𝘁𝗼𝗿𝗮𝗴𝗲
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚗𝚎𝚝𝚠𝚘𝚛𝚔 manages custom networks containers connect to.
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚟𝚘𝚕𝚞𝚖𝚎 creates sharable storage volumes containers can mount.
𝗠𝗮𝗶𝗻𝘁𝗲𝗻𝗮𝗻𝗰𝗲
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚜𝚢𝚜𝚝𝚎𝚖 𝚙𝚛𝚞𝚗𝚎 cleans up unused containers, images, volumes, etc.
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚛𝚖 deletes stopped containers.
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚒𝚗𝚜𝚙𝚎𝚌𝚝 shows in-depth info on a container.
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚜𝚝𝚊𝚝𝚜 provides real-time container resource usage stats.
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚙𝚜 lists running containers.
𝗗𝗼𝗰𝗸𝗲𝗿 𝗖𝗼𝗺𝗽𝗼𝘀𝗲
- 𝚍𝚘𝚌𝚔𝚎𝚛-𝚌𝚘𝚖𝚙𝚘𝚜𝚎 𝚞𝚙 starts a multi-container app from a compose file.
- 𝚍𝚘𝚌𝚔𝚎𝚛-𝚌𝚘𝚖𝚙𝚘𝚜𝚎 𝚍𝚘𝚠𝚗 stops and destroys the resources.
- 𝚍𝚘𝚌𝚔𝚎𝚛-𝚌𝚘𝚖𝚙𝚘𝚜𝚎 𝚕𝚘𝚐𝚜 aggregates logs from the containers.
𝗔𝗱𝗱𝗶𝘁𝗶𝗼𝗻𝗮𝗹 𝗖𝗼𝗺𝗺𝗮𝗻𝗱𝘀
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚌𝚙 copies files between host and containers.
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚍𝚒𝚏𝚏 shows filesystem changes in a container.
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚝𝚘𝚙 displays running processes in a container.
- 𝚍𝚘𝚌𝚔𝚎𝚛 𝚜𝚎𝚊𝚛𝚌𝚑 searches for images on Docker Hub.
Docker CLIs:
## for docker version
docker version
## to check no of container running
docker ps
## to check docker images
docker images
##Run a container using the redis image:
docker run redis
##Stop the container you just created:
docker stop <container-id>
##How many containers are PRESENT on the host now?Including both Running and Not Running ones:
docker ps -a
##What is the image used to run the nginx-1 container?
Run the docker ps command and check under the IMAGE column.
##What is the name of the container created using the ubuntu image?
Run the docker ps command and look at the NAMES column.
##What is the ID of the container that uses the alpine image and is not running?
Run the docker ps -a command and identify the ID of the container that uses alpine image.
##Delete all containers from the Docker Host.Both Running and Not Running ones. Remember you may have to stop containers before deleting them
To stop all the containers at once, run the command: docker stop $(docker ps -aq)
To remove all the stopped containers at once, run the command: docker rm $(docker ps -aq)
##Delete the ubuntu Image:
Run the command docker rmi ubuntu
##You are required to pull a docker image which will be used to run a container later. Pull the image nginx:1.14-alpine
Run the command docker pull nginx:1.14-alpine
##Run a container with the nginx:1.14-alpine image and name it webapp
Run the command docker run -d --name webapp nginx:1.14-alpine and check the status of created container by docker ps command.
##Cleanup: Delete all images on the host.Remove containers as necessary
Stop and delete all the containers being used by images.
Then run the command to delete all the available images: docker rmi $(docker images -aq)
$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
611162e0a78c nginx:1.14-alpine "nginx -g 'daemon of…" 4 minutes ago Exited (0) 2 minutes ago webapp
$
$ docker stop 611162e0a78c
611162e0a78c
$
$ docker rm 611162e0a78c
611162e0a78c
$
$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
$
$ docker rmi $(docker images -aq)
Untagged: nginx:1.14-alpine
Untagged: nginx@sha256:485b610fefec7ff6c463ced9623314a04ed67e3945b9c08d7e53a47f6d108dc7
Deleted: sha256:8a2fb25a19f5dc1528b7a3fabe8b3145ff57fe10e4f1edac6c718a3cf4aa4b73
Deleted: sha256:f68a8bcb9dbd06e0d2750eabf63c45f51734a72831ed650d2349775865d5fc20
Deleted: sha256:cbf2c7789332fe231e8defa490527a7b2c3ae8589997ceee00895f3263f0a8cf
Deleted: sha256:894f3fad7e6ecd7f24e88340a44b7b73663a85c0eb7740e7ade169e9d8491a4c
Deleted: sha256:a464c54f93a9e88fc1d33df1e0e39cca427d60145a360962e8f19a1dbf900da9
##Which of the ports are the exposed on the CONTAINER?
Run the command docker ps and look under the PORTS column. Ports on the right(after ->) are exposed on the container.
##Which of the ports are published on Host?
Run the command docker ps and look under the PORTS column. Ports on the left(before ->) are published on the host.
##Run an instance of kodekloud/simple-webapp with a tag blue and map port 8080 on the container to 38282 on the host.
$ docker run -p 38282:8080 kodekloud/simple-webapp:blue
##We just downloaded the code of an application. What is the base image used in the Dockerfile?Inspect the Dockerfile in the webapp-color directory
You can either open the file using vi /root/webapp-color/Dockerfile (or using commands such as cat/more/less/vim e.t.c) and look for the FROM instruction or search for it directly using grep -i FROM /root/webapp-color/Dockerfile
##To what location within the container is the application code copied to during a Docker build?
Inspect the Dockerfile in the webapp-color directory.
Open the Dockerfile and look for COPY command.
##When a container is created using the image built with this Dockerfile, what is the command used to RUN the application inside it.
Inspect the Dockerfile in the webapp-color directory.
Open the Dockerfile and look for ENTRYPOINT command
##Build a docker image using the Dockerfile and name it webapp-color. No tag to be specified.
Move to the directory first by using the cd command and verify the path of the working directory from pwd command
$ cd /root/webapp-color/
$ pwd
/root/webapp-color
Now, run the docker build command within that directory :-
$ docker build -t webapp-color .
##Run an instance of the image webapp-color and publish port 8080 on the container to 8282 on the host.
Command: docker run -p 8282:8080 webapp-color
##What is the base Operating System used by the python:3.6 image?If required, run an instance of the image to figure it out.
Run docker run python:3.6 cat /etc/*release* command.
##Build a new smaller docker image by modifying the same Dockerfile and name it webapp-color and tag it lite.Hint: Find a smaller base image for python:3.6. Make sure the final image is less than 150MB
Modify Dockerfile to use python:3.6-alpine image and then build using docker build -t webapp-color:lite .
##Inspect the environment variables set on the running container and identify the value set to the APP_COLOR variable.
To know the running containers, run the command docker ps and identify the running container name or container id.
Run this command to get the env fields from the inspect command: docker inspect <container-name> | grep -A 10 Env
Replace container-name with the correct one.
##Run a container named blue-app using image kodekloud/simple-webapp and set the environment variable APP_COLOR to blue. Make the application available on port 38282 on the host. The application listens on port 8080
Run the command : docker run -p 38282:8080 --name blue-app -e APP_COLOR=blue -d kodekloud/simple-webapp
To know the env field from within a webapp container, run docker exec -it blue-app env
##Deploy a mysql database using the mysql image and name it mysql-db.Set the database password to use db_pass123. Lookup the mysql image on Docker Hub and identify the correct environment variable to use for setting the root password.
Run the command: docker run -d -e MYSQL_ROOT_PASSWORD=db_pass123 --name mysql-db mysql
To know the env field from within a mysql-db container, run docker exec -it mysql-db env
##What is the ENTRYPOINT configured on the mysql image?
Run: cat Dockerfile-mysql | grep ENTRYPOINT
$ cat Dockerfile-mysql | grep ENTRYPOINT
ENTRYPOINT ["docker-entrypoint.sh"]
##What is the CMD configured on the wordpress image?
$ ls
Dockerfile-mysql Dockerfile-python Dockerfile-ubuntu Dockerfile-wordpress app
$
$ cat Dockerfile-wordpress | grep CMD
CMD ["apache2-foreground"]
##What is the final command run at startup when the wordpress image is run. Consider both ENTRYPOINT and CMD instructions
Open the file /root/Dockerfile-wordpress and inspect the both ENTRYPOINT + CMD instructions.
##What is the command run at startup when the ubuntu image is run?
Run: cat Dockerfile-ubuntu | grep CMD
$ cat Dockerfile-ubuntu | grep CMD
CMD ["bash"]
##Run an instance of the ubuntu image to run the sleep 1000 command at startup.Run it in detached mode.
$ docker run -d ubuntu sleep 1000
eeaf9457c45528e374f1ed607d944ce62a75a93249c5b8ce41fbf125771eb702
First create a redis database container called redis, image redis:alpine.
$ docker run --name redis -d redis:alpine
Unable to find image 'redis:alpine' locally
alpine: Pulling from library/redis
59bf1c3509f3: Pull complete
719adce26c52: Pull complete
b8f35e378c31: Pull complete
d034517f789c: Pull complete
3772d4d76753: Pull complete
211a7f52febb: Pull complete
Digest: sha256:4bed291aa5efb9f0d77b76ff7d4ab71eee410962965d052552db1fb80576431d
Status: Downloaded newer image for redis:alpine
05cfbd9839847667f2652b2e88aa259c4287c9145ff972f55dd05fcaaf2c95f3
Next, create a simple container called clickcounter with the image kodekloud/click-counter, link it to the redis container that we created in the previous task and then expose it on the host port 8085
The clickcounter app run on port 5000
$ docker run -d --name=clickcounter --link redis:redis -p 8085:5000 kodekloud/click-counter
Unable to find image 'kodekloud/click-counter:latest' locally
latest: Pulling from kodekloud/click-counter
540db60ca938: Already exists
a7ad1a75a999: Pull complete
37ce6546d5dd: Extracting [=================================================> ] 10.49MB/10.57MB
ec9e91bed5a2: Download complete
767433e10bb0: Download complete
156f0b0493cb: Download complete
3fe82d8a2401: Download complete
4a41f7c94204: Download complete
473063430a4f: Download complete
452c68a16ccd: Download complete
Digest: sha256:530e4532a718e8f5cbda05844a6c0638ebe8898fa4c4307ee6afbdd5d1f213db
Status: Downloaded newer image for kodekloud/click-counter:latest
52ea3950550080d1596d1ef70e0930f91453ea865f33dc732af1fc648e9139b1
Let's clean up the actions carried out in previous steps. Delete the redis and the clickcounter containers.
To stop the containers: docker stop <CONTAINER-NAME>
To delete the containers: docker rm <CONTAINER-NAME>
$ docker stop clickcounter
clickcounter
$ docker rm clickcounter
clickcounter
$ docker rm redis
Error response from daemon: You cannot remove a running container 05cfbd9839847667f2652b2e88aa259c4287c9145ff972f55dd05fcaaf2c95f3. Stop the container before attempting removal or force remove
docker stop 05cfbd9839847667f2652b2e88aa259c4287c9145ff972f55dd05fcaaf2c95f3
05cfbd9839847667f2652b2e88aa259c4287c9145ff972f55dd05fcaaf2c95f3
$ docker rm 05cfbd9839847667f2652b2e88aa259c4287c9145ff972f55dd05fcaaf2c95f3
05cfbd9839847667f2652b2e88aa259c4287c9145ff972f55dd05fcaaf2c95f3
##Create a docker-compose.yml file under the directory /root/clickcounter. Once done, run docker-compose up.
The compose file should have the exact specification as follows -
- redis service specification - Image name should be redis:alpine.
- clickcounter service specification - Image name should be kodekloud/click-counter, app is run on port 5000 and expose it on the host port 8085 in the compose file.
Use the below compose file:
services:
redis:
image: redis:alpine
clickcounter:
image: kodekloud/click-counter
ports:
- 8085:5000
version: '3.0'
Then run a docker-compose up -d command. To run containers in a background, added -d flag.
##What location are the files related to the docker containers and images stored?
$ ls /var/lib/docker
builder buildkit containerd containers image network overlay2 plugins runtimes swarm tmp trust volumes
##What directory under /var/lib/docker are the files related to the container alpine-3 image stored?
$ cd /var/lib/docker/containers/
$ ls
478adb8e835e0e03d5d95abba19b44c1182825b211abbd948b048f74cd6ceaa5 81f7a8bb1a567de73ba537834dbe75a33d3a3eee30052b73e9a095fe9f6c1538
4ba10cfbae7aeec4f9bb76fc8a4ef926b24f35dee397698125f3a7b0bf1a23a0
$
$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
478adb8e835e alpine "/bin/sh" About a minute ago Exited (0) About a minute ago alpine-3
81f7a8bb1a56 alpine "/bin/sh" About a minute ago Exited (0) About a minute ago alpine-2
4ba10cfbae7a alpine "/bin/sh" About a minute ago Exited (0) About a minute ago alpine-1
##Run a mysql container named mysql-db using the mysql image. Set database password to db_pass123
Note: Remember to run it in the detached mode.
$ docker run -d --name mysql-db -e MYSQL_ROOT_PASSWORD=db_pass123 mysql
134daac876ad80eb806e5abde9a893da2d3a44db44758965fd88263e8c60f0af
##We have just written some data into the database. To view the information we wrote, run the get-data.sh script available in the /root directory. How many customers data have been written to the database?
$ pwd
/var/lib/docker/containers
$ cd /root
$ sh get-data.sh
mysql: [Warning] Using a password on the command line interface can be insecure.
id Name Phone Email
1 Kareem 130-5655 Duis.volutpat.nunc@quamCurabitur.org
2 Ruby 1-584-149-0770 Nulla.tempor@vitaeorciPhasellus.org
3 Rowan 199-8663 consectetuer.adipiscing.elit@Sedmalesuada.co.uk
4 Alisa 220-6017 elementum.sem.vitae@enimMauris.edu
5 Ella 731-0337 fermentum@nec.net
6 Tiger 658-4480 quis.diam@odiovelest.net
7 Felix 1-274-848-3378 Mauris.vel@arcu.com
8 Karina 1-390-796-3451 sagittis.semper@odioapurus.co.uk
9 Davis 605-8539 venenatis.vel@risusDonecnibh.com
10 Mohammad 1-590-174-1489 ornare.sagittis.felis@natoque.ca
11 Zane 362-1770 Aenean.euismod@condimentum.co.uk
12 Piper 1-231-386-6903 nunc.sed.pede@nascetur.ca
13 Marshall 1-383-729-4990 Cras.interdum.Nunc@neceuismod.ca
14 Zena 241-6641 Fusce.mollis.Duis@lobortis.org
15 Abdul 1-748-387-9935 eget.lacus.Mauris@Crasvehicula.com
16 Chase 1-401-241-9169 ante.dictum.mi@nascetur.org
17 Zahir 921-0663 non@nonummyutmolestie.edu
18 Brenda 1-691-909-5827 Quisque.ac@magnaCras.co.uk
19 Laura 1-562-983-9565 Quisque.ornare.tortor@sollicitudinadipiscing.ca
20 Madison 1-348-737-0587 Quisque.varius@Intinciduntcongue.org
21 Tanek 991-6278 dignissim.magna@Pellentesqueutipsum.net
22 Dakota 893-0792 Nullam.enim.Sed@nulla.net
23 Boris 1-297-302-5792 non.sollicitudin@eleifendegestasSed.co.uk
24 Celeste 723-6729 mauris.rhoncus@eunulla.edu
25 Connor 1-203-901-7531 et@loremipsumsodales.edu
26 Perry 1-756-607-9187 eros.turpis@tristiquepharetra.co.uk
27 Hayfa 1-609-407-3019 non.lobortis.quis@malesuadafringilla.net
28 Todd 343-0454 id.erat@arcu.org
29 Fuller 881-7273 non.feugiat.nec@adipiscingelit.net
30 Rama 1-927-605-0610 nonummy.ultricies.ornare@malesuada.co.uk
##Run a mysql container again, but this time map a volume to the container so that the data stored by the container is stored at /opt/data on the host.
Use the same name : mysql-db and same password: db_pass123 as before. Mysql stores data at /var/lib/mysql inside the container.
$ docker run -v /opt/data:/var/lib/mysql -d --name mysql-db -e MYSQL_ROOT_PASSWORD=db_pass123 mysql
9c58ef00b9efdf85b11c741b9c594c0ed80b7063ffd96c5507c4fc2ec6c15694
##Disaster strikes.. again! And the database crashed again. But this time we have the data stored at /opt/data directory. Re-deploy a new mysql instance using the same options as before.
Just run the same command as before. Here it is for your convenience: docker run -v /opt/data:/var/lib/mysql -d --name mysql-db -e MYSQL_ROOT_PASSWORD=db_pass123 mysql
$ docker run -v /opt/data:/var/lib/mysql -d --name mysql-db -e MYSQL_ROOT_PASSWORD=db_pass123 mysql
f053ae4c9257f6f077f31bd8984ccfec18311f14eaf835cd94bf9461e08b3f58
Explore the current setup and identify the number of networks that exist on this system.
$ docker network ls
NETWORK ID NAME DRIVER SCOPE
497c0830787a bridge bridge local
5de628a52135 host host local
e32507f046e4 none null local
##We just ran a container named alpine-1. Identify the network it is attached to.
Run the command docker inspect alpine-1 and look under the Networks section.
##What is the subnet configured on bridge network?
Run the command docker network inspect bridge
##Run a container named alpine-2 using the alpine image and attach it to the none network.
$ docker run --name alpine-2 --network=none alpine
##Create a new network named wp-mysql-network using the bridge driver. Allocate subnet 182.18.0.1/24. Configure Gateway 182.18.0.1
Run the command: docker network create --driver bridge --subnet 182.18.0.1/24 --gateway 182.18.0.1 wp-mysql-network
Inspect the created network by docker network inspect wp-mysql-network
##Deploy a mysql database using the mysql:5.6 image and name it mysql-db. Attach it to the newly created network wp-mysql-network
Set the database password to use db_pass123. The environment variable to set is MYSQL_ROOT_PASSWORD.
Run the command: docker run -d -e MYSQL_ROOT_PASSWORD=db_pass123 --name mysql-db --network wp-mysql-network mysql:5.6
##Deploy a web application named webapp using the kodekloud/simple-webapp-mysql image. Expose the port to 38080 on the host.
The application makes use of two environment variable:
1: DB_Host with the value mysql-db.
2: DB_Password with the value db_pass123.
Make sure to attach it to the newly created network called wp-mysql-network.
Also make sure to link the MySQL and the webapp container.
Run the command: docker run --network=wp-mysql-network -e DB_Host=mysql-db -e DB_Password=db_pass123 -p 38080:8080 --name webapp --link mysql-db:mysql-db -d kodekloud/simple-webapp-mysql
