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For docker users, the best case is that they do not need to create their own images. Almost all commonly used databases, middleware, applications, etc., have ready-made official docker images or images created by other people and organizations. We only need a little configuration to use them directly.

But in some cases, you also need to build your own image.

For example:

1. Cannot find a ready-made image, such as developing your own application.

2. Specific functions need to be added to the image.

Docker provides two ways to build an image: the docker commit command and the Dockerfile build file.

Docker commit

Docker commit imperative is the most intuitive way to create an image, which consists of three steps

1. Run the container

2. Modify the container

3. Save the container as a new image

For example, install vi in the Ubuntu base image and save it as a new image

(1) run the container

The action of the-it parameter enters the container in interactive mode and opens the terminal.

2b1763cc8299 is the ID inside the container.

(2) install vim

Confirm that vim is not installed

Install vim as follows:

(3) Save as a new image

View the currently running container in a new window

Distracter_chaum is the name that Docker randomly assigned to our container.

Execute the docker commit command to save the container as a mirror

The new image is named ubuntu-with-vim

View the properties of the new mirror, as follows:

You can see that the new image has become larger because of the installation of vim software.

Launch the container from the new image and verify that vim is ready to use

Although we can use docker commit to create new images, docker does not recommend that users build images in this way. The reasons are as follows:

1. This method is a manual way to create a mirror image, which is prone to error, low efficiency and weak repeatability.

2. Unable to audit the image, there is a security risk.

Dockerfile

Dockerfile is a text file that records all the steps of building an image

The first Dockerfile

Create a new text file, Dockerfile, with the following contents:

The following is to run the docker build command to build the image and analyze the details in detail

[root@docker-1] # docker build-t ubuntu-with-vim-dockerfile. (1) Sending build context to Docker daemon 13.31kB (2) Step 1 vim 2: FROM ubuntu (3)-> a2a15febcdf3Step 2 Acer 2: RUN apt-get update & & apt-get install-y vim (4)-> Running in ad7fa94cfb94 (5) Successfully built ad7fa94cfb94 (6) Successfully tagged ubuntu-with-vim-dockerfile:latest (7)

Description:

1. Run the docker build command, and-t name the new image at the end of the ubuntu-with-vim-dockerfile command. Indicates that build context is the current directory. By default, Docker looks for Dockerfile files from build context.

You can also specify the location of the Dockerfile file with the-f parameter

2. The process of image construction. First, Docker sends the files in the build context to Docker daemon,bulid context to provide the files or targets needed for the image build. The ADD,COPY command in Dockerfile adds files from build context to the image. In this case, bulid context is the current directory. Root, and all files and subdirectories in that directory are sent to Docker daemon. Be careful not to put extra files into bulid context, especially /, / usr as bulid context, otherwise the build process will be quite slow or even fail

3. Step1, execute FROM, take Ubuntu as base image, and mirror ID as a2a15febcdf3

4. Step2, execute RUN, install vim

5. Start the temporary container and install vim through apt-get in the container

6. After the installation is completed, save the container as an image, and its ID is ad7fa94cfb94

The bottom layer of this step uses a command similar to docker commit

7. The image is built successfully

View image information through docker images

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