In this blog, I will try to provide you with a complete cheat sheet on Docker CLI & YAML so that you can quickly revise the Docker without wasting any time.
This blog is intended for those who have learnt Docker Previously and want to revise that.
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Dockerfile
It's just a text file that contains instructions for building a Docker image.
It's just to automate the process that you do manually. So if you know how to do a process manually, you can learn it quickly.
Format
INSTRUCTION arguments
Instruction Set
In the below table, I have mentioned some sort terms. dir -> Directory, src -> Source, dst -> Destination
| INSTRUCTION | DESCRIPTION |
|---|---|
| FROM <image_name> | Fetch base image for Docker |
| COPY <src_dir_host> <dest_dir_container> | Copy a folder of the host system to the container |
| WORKDIR <dir_path_contaiiner> | Set the working directory of the container where the commands will run |
| RUN <command> | Run commands in a shell |
| RUN [<command arg1>, <command arg2>] | We can break the command in command args also. |
Ex : RUN "apt-get update" -> RUN ["apt-get", "update"]
|
|
| ENV <key>=<value> | Set environment variables |
| EXPOSE <container_port> | Expose the port of a container to make it accessible in the same network |
| ENTRYPOINT <command> | That command will execute as soon as the container boot up |
| ENTRYPOINT [<command arg1>, <command arg2>] | We can break the command in command args also. |
Ex : RUN "/bin/sh sample.sh" -> RUN ["/bin/sh", "sample.sh"]
|
There is one more command, which you see mostly. CMD
The purpose of this command is to run the commands specified in arguments. It also has two formats, for example.
CMD echo "hello-world."
CMD ["/bin/sh", "echo", "hello-world"]
You might be confused now about the difference between RUN and CMD.
RUNruns all the commands specified in the argument-
For
CMDthere is some particular case.- If you have provided some commands to run in
docker runcommand,CMDis going to be ignored. - If you have listed multiple CMD statements, only the last CMD will be executed.
- IF
ENTRYPOINTin Dockerfile is provided,CMDit is going to be ignored. - In any container deployment platform, you can see the
CMDto run manually.
- If you have provided some commands to run in
🔵 As the blog's purpose is to give concise details of Dockerfile and CLI, we are not attaching Dockerfile examples here. But will create some blogs on Dockerfile and attach links to them.
Docker CLI
Arguments List
Argument |
Description |
-u |
Username |
--name |
Name [Normally used for container] |
-d |
Detach [Run in the background] |
-a |
All [Stopped + Paused + Running] |
-i |
Interactive |
-t |
- tty [stdin] [For Container] |
-it |
Interactive with stdin |
-w |
Working directory [example -w '/opt/test'] |
-p |
Port [Example : -p <host_system_port>:<container_port> ] |
-v |
Volume Mount [Example : -p <host_system_volume_path>:<container_volume_path> ] |
-e |
Environment Variable [Example : -e <variable_name>=<value> ] |
Image Specific Commands
List all local images
docker images
Build Image From Dockerfile in current directory
docker build . -t <tag_name>
Pull an image from Dockerhub
docker pull <image_name>
# example : docker pull redis
Delete an image
docker rmi redis
Remove all unused images
docker image prune
Container Specific Commands
Run a docker container from an image
docker run <image_name>
Now you can refer the Arguments List table to choose your required arguments
I am solving an question for example.
Let's assume, I need to create an container from image of redis with port mapping from container port 6379 to host port 6379 . The name will be redis-instance-1 . Make the instance detachable & run
redis-server --requirepass "SECRET_PASSWORD"at its beginning.docker run --name redis-instance-1 -d -p 6379:6379 redis redis-server --requirepass "SECRET_PASSWORD"Its important to notice that , you need to pass all the arguments before providing the image name and entrypoint_command
List containers [only Running]
docker ps
List all containers [Stopped + Paused + Running]
docker ps -a
Start or Stop a container
docker start|stop <container_name or container_id>
You can get the
Container IDby running the command for list all container
Remove a stopped container
docker rm <container_name or container_id>
Attach to the current process of container
docker attach <container_name or container_id>
Run a command in the container
docker exec <container_name or container_id> <command>
Example : Start a bash terminal in redis instance
docker exec -it redis /bin/sh
❓You may have a question. What's the difference between exec and attach, then
With attach, we attach to the process that's currently running in the container
But with exec, we can run a new process in a container without hampering the running process of the container
Log the data of the current process of the container
docker logs -f <container_name or container_id>
Inspect and grab all the details of a container
docker inspect <container_name or container_id>
It will return the details in an JSON format
Check the stats [CPU, RAM, Network, Storage usage] for all running containers
docker container stats
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