Debug School: Tomar Singh

Docker tmpfs volume by Tomar

Tomar Singh — Wed, 16 Nov 2022 05:15:00 +0000

How can we store container data in memory using docker volume
We use docker tmpfs volume to store container data in host's memory. As we are storing this in memory it will be volatile. Also we can not attach this volume with some other container because we don't know the Physical location in this case.

Example:
docker run -itd --name tmpfstest --tmpfs /var/tmpfs ubuntu

Now if we inspect this container, we will get following in output:
"Tmpfs": {
"/var/tmpfs": ""
}

Docker image by Tomar

Tomar Singh — Tue, 15 Nov 2022 06:44:00 +0000

What is a Docker image. Explain in 10 points.

Docker image consists multiple file system.
It is a name inside repository and this name will be linked to docker Layer ID.
This Layer Id is used to recognize the parents for that layer and so on.
Docker images will have multiple layers. The rootfile System or base image at the bottom layer and then there will be multiple layers on top it for software and applications.
When a docker image is pulled these data layers will stored in docker locally (inside overlay2 - again depends on the filesystem type), and meta layers will be there in images directory.
When we create a container using this image all layers will be merged and mounted to the user attached with container.
If are creating any new file in container, it will be stored at two places diff and merge.
mount for an image is conmbination of diff and image layers.
when you stop a container the merge directory go away.

Docker Update and wait by Tomar

Tomar Singh — Tue, 15 Nov 2022 05:15:40 +0000

What is the use of "docker update"?

Docker update command is used to update the container resources or configuration at runtime. It can change cpu or memory initial configuration like this: docker update -m 512m

This command can help us in scenarios where more resources require for a container Or if container is under performing.

What is the use of "docker wait"?

docker wait command is used to wait until the command executes (until the mentioned container stops). For example if a container is going to stop wait command will block your terminal for any operation until it stops successfully. -> docker wait
this will block the terminal. Now if go to the other terminal and stops this container, docker wait command will return 0 and terminal will be available for further use.

Docker Lab Assignment - Tomar

Tomar Singh — Mon, 14 Nov 2022 10:11:37 +0000

what is the diff between docker pause and docker unpause?

docker pause will stop the processes inside the specified container. Its not going to use resources (cpu ,memory), On the other hand unpause will again resume the process. After pausing a container if you do docker stats, it will show that cpu has 0% of utilization. When we unpause it, cpu usage shows 0.1% of usage.

What is the diff between docker stop and docker kill?

docker stop commands will not stop processes immediately, it will gracefully handle it. docker stop SIGTERM command. Whereas docker kill will suspends the process immediately by sending SIGKILL command, thats why we see zero (0) for killed container.

Docker Summary by Tomar

Tomar Singh — Mon, 14 Nov 2022 07:26:33 +0000

What is Docker?

Docker is containerization management tool which allow you to perform certain operations on container like - create, stop, pause etc. It is a tool which talks to kernel using various components.

Why Docker?

Docker is a way to interact with OS Kernel for performing various container operation. Containers are important to run multiple instance of same image.

What is Container?

It is not possible to run the same application multiple times (for ex running 3 apache instances) in PC environment. To overcome this issue we have something called Container. Containers run your application by sharing the resources and have its own Users, PID, network tree and file system.

Docker workflow?

Docker client -> Rest APIs -> Docker Server (server checks the required image if not there then connects to registry to get it).

How container created?

Containers are created by OS kernel on demand by Docker. Docker gives instructions to kernel to creates Users, PID, Network tree, File system and then connect the created user to these components.