{"id":114,"date":"2023-10-13T10:46:02","date_gmt":"2023-10-13T09:46:02","guid":{"rendered":"https:\/\/technology.corporatesstore.com\/?page_id=114"},"modified":"2023-11-03T07:34:31","modified_gmt":"2023-11-03T07:34:31","slug":"docker-overview","status":"publish","type":"page","link":"https:\/\/technology.corporatesstore.com\/index.php\/devops-culture\/docker-overview\/","title":{"rendered":"Docker Overview"},"content":{"rendered":"\n

Docker vs Virtual Machines<\/strong><\/p>\n\n\n\n

While Docker and virtual machines serve a similar purpose, their performance, OS support, and portability differ significantly.<\/p>\n\n\n\n

The main difference is that Docker containers share the host\u2019s operating system, while virtual machines also have a guest operating system running on top of the host system. This method of operation affects the performance, hardware needs, and OS support. Check the table below for an in-depth comparison.<\/p>\n\n\n\n

Criteria<\/th>Docker<\/th>Virtual Machine<\/th><\/tr><\/thead>
OS<\/td>Shared OS between containers.<\/td>New OS for each VM.<\/td><\/tr>
Security<\/td>Less secure because the operating system and kernel are shared.<\/td>More secure as VMs don\u2019t share the operating system.<\/td><\/tr>
Performance<\/td>Fast performance even with several containers.<\/td>More virtual machines equal less stable performance.<\/td><\/tr>
Boot-up time<\/td>Fast (seconds).<\/td>Slow (minutes).<\/td><\/tr>
Memory needs<\/td>Lightweight.<\/td>Require a lot of memory.<\/td><\/tr>
Storage needs<\/td>Usually megabytes.<\/td>Usually gigabytes.<\/td><\/tr>
Portability<\/td>Easy to deploy in different environments.<\/td>Hard to port a VM to another system.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Even though Docker\u2019s container technology comes on top in most aspects, virtual machines are more secure because the OS is kept independent from the hardware.<\/p>\n\n\n\n

Docker vs Docker Engine<\/strong><\/p>\n\n\n\n

Docker is the name of the platform, while Docker Engine is an open-source container technology that consists of a Docker server (daemon), client, and APIs. People might also confuse the software with the Docker client because it\u2019s also called docker<\/strong>, only in lowercase letters.<\/p>\n\n\n\n

Removing All Unused Docker Resources<\/strong><\/p>\n\n\n\n

Docker doesn\u2019t remove any unused data by itself, which can result in cluttering your disk space.<\/p>\n\n\n\n

If you\u2019d like to remove all images, containers, and networks that are not associated with a container,<\/p>\n\n\n\n

docker system prune<\/strong><\/p>\n\n\n\n

This command will remove everything<\/strong>, including dangling images and stopped containers, as the following message will tell you:<\/p>\n\n\n\n

WARNING! This will remove:<\/p>\n\n\n\n

– all stopped containers <\/p>\n\n\n\n

– all networks not used by at least one container <\/p>\n\n\n\n

– all dangling images <\/p>\n\n\n\n

– all dangling build cache<\/p>\n\n\n\n

Are you sure you want to continue? [y\/N]<\/p>\n\n\n\n

In order to include all unused images, execute the following command:<\/p>\n\n\n\n

docker system prune -a<\/strong><\/p>\n\n\n\n

Here\u2019s the warning message that you\u2019ll see before continuing:<\/p>\n\n\n\n

WARNING! This will remove:<\/p>\n\n\n\n

– all stopped containers<\/p>\n\n\n\n

– all networks not used by at least one container<\/p>\n\n\n\n

– all images without at least one container associated to them<\/p>\n\n\n\n

– all build cache<\/p>\n\n\n\n

Are you sure you want to continue? [y\/N]<\/p>\n\n\n\n

However, the previous two commands will not touch unused volumes \u2013 this is done deliberately for safety reasons.<\/p>\n\n\n\n

If you\u2019d like to remove that as well, use the following command:<\/p>\n\n\n\n

docker system prune –volumes<\/strong><\/p>\n\n\n\n

Docker Objects<\/strong><\/p>\n\n\n\n

When you use Docker, you are creating and using images, containers, networks, volumes, plugins, and other objects. This section is a brief overview of some of those objects.<\/p>\n\n\n\n

Docker Container<\/strong><\/p>\n\n\n\n

Docker is among the most popular open-source container-based tools. It is used to run instances of Docker images since these create a new Docker container.<\/p>\n\n\n\n

In other words, images can be considered as a template that can be used to create containers. They contain information about what\u2019s required to develop and run a container. Another excellent image feature is that multiple images can be stored locally or remotely.<\/p>\n\n\n\n

A container is a runnable instance of an image. You can create, start, stop, move, or delete a container using the Docker API or CLI. You can connect a container to one or more networks, attach storage to it, or even create a new image based on its current state.<\/p>\n\n\n\n

By default, a container is relatively well isolated from other containers and its host machine. You can control how isolated a container’s network, storage, or other underlying subsystems are from other containers or from the host machine.<\/p>\n\n\n\n

A container is defined by its image as well as any configuration options you provide to it when you create or start it. When a container is removed, any changes to its state that aren’t stored in persistent storage disappear.<\/a><\/p>\n\n\n\n

Create a Docker Container<\/strong><\/p>\n\n\n\n

In this section, we will use the Ubuntu 20.04<\/strong> virtual private server and assume you already have Docker installed. Therefore, start by accessing your VPS via SSH.<\/p>\n\n\n\n

To list all Dockers images on your system, you can use the following command:<\/p>\n\n\n\n

sudo docker images<\/strong><\/p>\n\n\n\n

If you want to display additional information, enter the following command in the command line:<\/p>\n\n\n\n

sudo docker images –help<\/strong><\/p>\n\n\n\n

Let’s say we don\u2019t have any Docker images on our system, so let\u2019s pull a new one first.<\/p>\n\n\n\n

To do that, first, go to the Docker Hub. Here you will find thousands of Docker base images.<\/p>\n\n\n\n

In this example, we will pull a MySQL image. Note that you can browse each image\u2019s page to see more details about the image.<\/p>\n\n\n\n

\"\"\/<\/figure>\n\n\n\n

You can pull the new image to the current directory with the command:<\/p>\n\n\n\n

docker pull <image name or image id><\/strong><\/p>\n\n\n\n

Using the -q<\/strong> option will list only numeric IDs of images available on your system:<\/p>\n\n\n\n

sudo docker images -q<\/strong><\/p>\n\n\n\n

-f<\/strong> is the filter flag. If you want to list all images that are not dangling (tagged or referenced by a new container), use the following command in the command line:<\/p>\n\n\n\n

sudo docker images -f ‘dangling=false’<\/strong><\/p>\n\n\n\n

Now that you know how to pull and locate an image to start a Docker container, it\u2019s time to run it. By running an image, you will create a container out of that image.<\/p>\n\n\n\n

To start a Docker container, use the docker run<\/strong> command:<\/p>\n\n\n\n

docker run <image_name><\/strong><\/p>\n\n\n\n

We will run the MySQL image. As such, the command will be:<\/p>\n\n\n\n

docker run mysql<\/strong><\/p>\n\n\n\n

Our container is created but not started. To start it, use this command via the command prompt:<\/p>\n\n\n\n

docker run –name MyContainer -it mysql bash<\/strong><\/p>\n\n\n\n

Here \u2013name MyContainer<\/strong> is how we wish to call the running process, while -it mysql bash<\/strong> names which container we are running.<\/p>\n\n\n\n

Now, open another terminal window. SSH into the server, and run the Docker ps<\/strong> command:<\/p>\n\n\n\n

sudo docker ps -a<\/strong><\/p>\n\n\n\n

As you can see, the container named MyContainer<\/strong> is now running. To stop the container, issue the following command:<\/p>\n\n\n\n

sudo docker stop MyContainer<\/strong><\/p>\n\n\n\n

If you wish to see the top process of a container, we can run this command:<\/p>\n\n\n\n

docker top MyContainer<\/strong><\/p>\n\n\n\n

MyContainer<\/strong> represents your container name.<\/p>\n\n\n\n

\"\"\/<\/figure>\n\n\n\n

To see additional stats, such as container ID, CPU utilization, or memory usage, use this command:<\/p>\n\n\n\n

docker stats<\/strong><\/p>\n\n\n\n

\"\"\/<\/figure>\n\n\n\n

Lastly, if you need to terminate a Docker container, use the following:<\/p>\n\n\n\n

sudo docker kill MyContainer<\/strong><\/p>\n\n\n\n

That\u2019s all there is to it \u2013 our Docker container is now ready to use.<\/p>\n\n\n\n

Remove Docker Containers<\/strong><\/p>\n\n\n\n

In order to see the list of all Docker containers, you will need to run this command:<\/p>\n\n\n\n

docker container ls -a<\/strong><\/p>\n\n\n\n

If you want to remove a specific container, enter the CONTAINER ID<\/strong> as shown in this example:<\/p>\n\n\n\n

docker container rm CONTAINER_ID<\/strong><\/p>\n\n\n\n

To remove all the containers that stopped<\/strong> in the application, follow this command:<\/p>\n\n\n\n

docker container prune<\/strong><\/p>\n\n\n\n

Take note that this will remove all stopped containers. In order to view the list of what containers will be deleted using the before mentioned command, use the \u2013filter <\/strong>flag:<\/p>\n\n\n\n

docker container ls -a –filter status=created –filter status=exited<\/strong><\/p>\n\n\n\n

To limit the removal of containers that stopped, for example, according to the time frame, you can use the following command:<\/p>\n\n\n\n

docker container prune –filter “until=24h”<\/strong><\/p>\n\n\n\n

If you want to remove a container once you\u2019re done working with it, you start one by adding a \u2013rm<\/strong> flag. Here\u2019s an example of how to remove such container:<\/p>\n\n\n\n

docker run –rm CONTAINER_ID<\/strong><\/p>\n\n\n\n

When you\u2019re done, the container will be deleted automatically.<\/p>\n\n\n\n

Docker Hub<\/strong><\/p>\n\n\n\n

To make image sharing easier, Docker came up with a streamlined image-sharing platform \u2013 Docker Hub. Here users can easily share, upload and manage their images.<\/p>\n\n\n\n

No matter the operating system you use, whether it\u2019s Ubuntu<\/strong> on a virtual instance<\/strong> or Windows<\/strong>, users will still be able to find popular images like MySQL<\/strong> or WordPress<\/strong> on Docker Hub.<\/p>\n\n\n\n

Users can always pick the paid version of Docker Hub if the free version proves to be lacking. It offers more robust features, vulnerability scans, and concurrent builds.<\/p>\n\n\n\n

Docker Hub is a registry service on the cloud that allows you to download Docker images that are built by other communities. You can also upload your own Docker built images to Docker hub.<\/p>\n\n\n\n

Docker Hub Login<\/strong><\/p>\n\n\n\n

The official site for Docker hub is \u2212 https:\/\/www.docker.com\/community-edition#\/add_ons<\/a><\/p>\n\n\n\n

First you need to do a simple sign-up on Docker hub.<\/p>\n\n\n\n

\"\"\/<\/figure>\n\n\n\n

Once you have signed up, you will be logged into Docker Hub.<\/p>\n\n\n\n

\"\"\/<\/figure>\n\n\n\n

Browse Jenkins Image<\/strong><\/p>\n\n\n\n

Next, let\u2019s browse and find the Jenkins image.<\/p>\n\n\n\n

\"\"\/<\/figure>\n\n\n\n

Run Jenkins<\/strong><\/p>\n\n\n\n

You can see the Docker pull<\/strong> command. This will be used to download the Jenkins image onto the local server.<\/p>\n\n\n\n

Now, go to the Ubuntu server and run the following command:<\/p>\n\n\n\n

sudo docker pull jenkins\/jenkins<\/strong><\/p>\n\n\n\n

\"\"\/<\/figure>\n\n\n\n

To run Jenkins, you need to run the following command:<\/p>\n\n\n\n

sudo docker run -p 8080:8080 -p 50000:50000 jenkins<\/strong><\/p>\n\n\n\n

Note the following points about the above sudo command:<\/p>\n\n\n\n