john_a – Best DevOps

Things to know about Docker

john_a — Tue, 17 Aug 2021 07:24:06 +0000

Docker images are basically a collection of filesystems
One copy of an image of gets mounted to each container
Images can be stored in a repository for use by other orgs
Docker images can contain one or more filesystems
Each filesystem in a docker image is called a layer
The base layer is always the root filesystem
When multiple layers exist in a docker image, the top layer will get priority
When we create a container, all layers get merged into a single layer that gets attached to the container
Docker images are stored in registries under the same name
When docker containers are stopped, they do not reflect changes made to filesystem while running

Docker Wait and Docker Update explained

john_a — Tue, 17 Aug 2021 05:31:11 +0000

Docker Update

The docker update command dynamically updates container configuration. We can use this command to prevent containers from consuming too many resources from their Docker host. With this command, we can place limits on a single container or on many.

docker update [OPTIONS] <container_name>

Before update cpu shares option –

After update cpu shares option –

Docker Wait

Block until one or more containers stop, then print their exit codes

docker wait <container_name>

Example of running docker wait – Start a container in the background.

$ docker run -dit --name=mine ubuntu bash

Run docker wait, which should block until the container exits.

$ docker wait mine

In another terminal, stop the first container. The docker wait command above returns the exit code.

$ docker stop mine

This is the same docker wait command from above, but it now exits, returning 0.

$ docker wait mine

0

Assignment Day 1 – John

john_a — Mon, 16 Aug 2021 10:01:01 +0000

What is the difference between docker pause and docker unpause?

The command “docker pause” suspends all processes in the specified containers. Usually the SIGSTOP signal is sent to the process, which is observable by the process being suspended. However, the command “docker unpause” automatically un-suspends the processes in the specified containers. Usually this is accomplished via the SIGCONT signal.

docker pause <container_name>
docker unpause <container_name>

What is the difference between docker stop and docker kill?

The command “docker stop” sends a SIGTERM signal to the main process inside the specified container and after a grace period will send a SIGKILL signal to the main process. The SIGTERM signal being sent first allows for a graceful cleanup of the process. However, the command “docker kill” sends a SIGKILL signal to the main process inside the specified container. This will automatically kill the main process without no timeout period.

docker stop <container_name>
docker kill <container_name>