Docker Image Usage-ApiDemos™

Docker Image Usage

When running a container with an image that does not exist locally, docker automatically downloads it from the docker image repository, by default from the Docker Hub public image source.

Let’s learn how to.

managing and using local Docker host images
Creating mirrors

List mirrors

We can use docker images to list the images on the local host.

apidemos@apidemos:~$ docker images           
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
ubuntu              14.04               90d5884b1ee0        5 days ago          188 MB
php                 5.6                 f40e9e0f10c8        9 days ago          444.8 MB
nginx               latest              6f8d099c3adc        12 days ago         182.7 MB
mysql               5.6                 f2e8d6c772c0        3 weeks ago         324.6 MB
httpd               latest              02ef73cf1bc0        3 weeks ago         194.4 MB
ubuntu              15.10               4e3b13c8a266        4 weeks ago         136.3 MB
hello-world         latest              690ed74de00f        6 months ago        960 B
training/webapp     latest              6fae60ef3446        11 months ago       348.8 MB

Description of each option:

REPOSITORY: indicates the repository source of the mirror
TAG: the label of the mirror
IMAGE ID: Mirror ID
CREATED: mirror creation time
SIZE: mirror size

The same repository source can have multiple TAGs, representing different versions of this repository source, such as the ubuntu repository source, there are many different versions of 15.10, 14.04, etc., we use REPOSITORY:TAG to define different mirrors.

So, if we want to run the container with the ubuntu system image of version 15.10, the command is as follows

apidemos@apidemos:~$ docker run -t -i ubuntu:15.10 /bin/bash 
root@d77ccb2e5cca:/#

Parameter description.

-i: Interactive operation.
-t: terminal.
ubuntu:15.10: This means to start the container with the ubuntu 15.10 image as the base.
/bin/bash: after the image name is the command, here we want to have an interactive shell, so we use /bin/bash.

If you want to run the container using the ubuntu system image with version 14.04, the command is as follows.

apidemos@apidemos:~$ docker run -t -i ubuntu:14.04 /bin/bash 
root@39e968165990:/#

If you do not specify a version tag for an image, for example if you only use ubuntu, docker will default to the ubuntu:latest image.

Get a new image

When we use a non-existent image on the local host, Docker will automatically download the image. If we want to pre-download the image, we can use the docker pull command to download it.

Capidemos@apidemos:~$ docker pull ubuntu:13.10
13.10: Pulling from library/ubuntu
6599cadaf950: Pull complete 
23eda618d451: Pull complete 
f0be3084efe9: Pull complete 
52de432f084b: Pull complete 
a3ed95caeb02: Pull complete 
Digest: sha256:15b79a6654811c8d992ebacdfbd5152fcf3d165e374e264076aa435214a947a3
Status: Downloaded newer image for ubuntu:13.10

Once the download is complete, we can use this image to run the container directly.

Find Mirror

We can search for mirrors from the Docker Hub website, which is located at https://hub.docker.com/.

We can also use the docker search command to search for mirrors. For example, we need an httpd image for our web service. We can use the docker search command to search for httpd to find the right image for us.

apidemos@apidemos:~$  docker search httpd

Docker Image Usage

NAME: The name of the mirror repository source

DESCRIPTION: Description of the mirror

OFFICIAL: whether it is an official docker release

stars: Similar to star in Github, means like, like.

AUTOMATED: Automatic build.

Drag and drop images

We decided to use the official httpd version of the image above and use the command docker pull to download the image.

apidemos@apidemos:~$ docker pull httpd
Using default tag: latest
latest: Pulling from library/httpd
8b87079b7a06: Pulling fs layer 
a3ed95caeb02: Download complete 
0d62ec9c6a76: Download complete 
a329d50397b9: Download complete 
ea7c1f032b5c: Waiting 
be44112b72c7: Waiting

Once the download is complete, we are ready to use the image.

apidemos@apidemos:~$ docker run httpd

Delete mirror

Mirror deletion is done using the docker rmi command, for example we delete the hello-world mirror by.

$ docker rmi hello-world

Docker Image Usage

Creating mirrors

When the image we downloaded from the docker image repository doesn’t meet our needs, we can make changes to the image in the following two ways.

1. Update the image from an already created container and commit the image
1. Use the Dockerfile command to create a new image

Update mirror

Before updating the image, we need to create a container using the image.

apidemos@apidemos:~$ docker run -t -i ubuntu:15.10 /bin/bash
root@e218edb10161:/#

Use the apt-get update command within the running container to perform the update.

When you are done, enter the exit command to exit the container.

At this point, the container with ID e218edb10161 is the container that has been changed as per our requirements. We can commit a copy of the container by using the command docker commit.

apidemos@apidemos:~$ docker commit -m="has update" -a="apidemos" e218edb10161 apidemos/ubuntu:v2
sha256:70bf1840fd7c0d2d8ef0a42a817eb29f854c1af8f7c59fc03ac7bdee9545aff8

Description of each parameter.

-m: Description information for the submission
-a: Specify the mirror author
e218edb10161: container ID
apidemos/ubuntu:v2: specifies the name of the target image to be created

We can use the docker images command to view our new image apidemos/ubuntu:v2.

apidemos@apidemos:~$ docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
apidemos/ubuntu       v2                  70bf1840fd7c        15 seconds ago      158.5 MB
ubuntu              14.04               90d5884b1ee0        5 days ago          188 MB
php                 5.6                 f40e9e0f10c8        9 days ago          444.8 MB
nginx               latest              6f8d099c3adc        12 days ago         182.7 MB
mysql               5.6                 f2e8d6c772c0        3 weeks ago         324.6 MB
httpd               latest              02ef73cf1bc0        3 weeks ago         194.4 MB
ubuntu              15.10               4e3b13c8a266        4 weeks ago         136.3 MB
hello-world         latest              690ed74de00f        6 months ago        960 B
training/webapp     latest              6fae60ef3446        12 months ago       348.8 MB

Start a container using our new image apidemos/ubuntu

apidemos@apidemos:~$ docker run -t -i apidemos/ubuntu:v2 /bin/bash                            
root@1a9fbdeb5da3:/#

Building an image

We use the command docker build to create a new image from scratch. To do this, we need to create a Dockerfile file that contains a set of instructions to tell Docker how to build our image.

apidemos@apidemos:~$ cat Dockerfile 
FROM    centos:6.7
MAINTAINER      Fisher "fisher@sudops.com"

RUN     /bin/echo 'root:123456' |chpasswd
RUN     useradd apidemos
RUN     /bin/echo 'apidemos:123456' |chpasswd
RUN     /bin/echo -e "LANG=\"en_US.UTF-8\"" >/etc/default/local
EXPOSE  22
EXPOSE  80
CMD     /usr/sbin/sshd -D

Each command creates a new layer on the mirror, and each command must be prefixed with a capital letter.

The first FROM, specifies which mirror source to use

The RUN directive tells docker what commands to execute inside the image, and what is installed.

Then, we use the Dockerfile file to build an image with the docker build command.

apidemos@apidemos:~$ docker build -t apidemos/centos:6.7 .
Sending build context to Docker daemon 17.92 kB
Step 1 : FROM centos:6.7
 ---> d95b5ca17cc3
Step 2 : MAINTAINER Fisher "fisher@sudops.com"
 ---> Using cache
 ---> 0c92299c6f03
Step 3 : RUN /bin/echo 'root:123456' |chpasswd
 ---> Using cache
 ---> 0397ce2fbd0a
Step 4 : RUN useradd apidemos
......

Parameter description.

-t : Specify the name of the target image to be created
. : the directory where the Dockerfile file is located, you can specify the absolute path of the Dockerfile

Use docker images to see that the created image already exists in the list, the image ID is 860c279d2fec

apidemos@apidemos:~$ docker images 
REPOSITORY          TAG                 IMAGE ID            CREATED              SIZE
apidemos/centos       6.7                 860c279d2fec        About a minute ago   190.6 MB
apidemos/ubuntu       v2                  70bf1840fd7c        17 hours ago         158.5 MB
ubuntu              14.04               90d5884b1ee0        6 days ago           188 MB
php                 5.6                 f40e9e0f10c8        10 days ago          444.8 MB
nginx               latest              6f8d099c3adc        12 days ago          182.7 MB
mysql               5.6                 f2e8d6c772c0        3 weeks ago          324.6 MB
httpd               latest              02ef73cf1bc0        3 weeks ago          194.4 MB
ubuntu              15.10               4e3b13c8a266        5 weeks ago          136.3 MB
hello-world         latest              690ed74de00f        6 months ago         960 B
centos              6.7                 d95b5ca17cc3        6 months ago         190.6 MB
training/webapp     latest              6fae60ef3446        12 months ago        348.8 MB

We can use the new image to create the container

apidemos@apidemos:~$ docker run -t -i apidemos/centos:6.7  /bin/bash
[root@41c28d18b5fb /]# id apidemos
uid=500(apidemos) gid=500(apidemos) groups=500(apidemos)

From above you can see that the new image already contains the user we created, apidemos.

Setting the image tag

We can use the docker tag command to add a new tag to the image.

apidemos@apidemos:~$ docker tag 860c279d2fec apidemos/centos:dev

docker tag The image ID, in this case 860c279d2fec , the user name, the image repository name, and the new tag name.

Using the docker images command, you can see that the image with ID 860c279d2fec has one more tag.

apidemos@apidemos:~$ docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
apidemos/centos       6.7                 860c279d2fec        5 hours ago         190.6 MB
apidemos/centos       dev                 860c279d2fec        5 hours ago         190.6 MB
apidemos/ubuntu       v2                  70bf1840fd7c        22 hours ago        158.5 MB
ubuntu              14.04               90d5884b1ee0        6 days ago          188 MB
php                 5.6                 f40e9e0f10c8        10 days ago         444.8 MB
nginx               latest              6f8d099c3adc        13 days ago         182.7 MB
mysql               5.6                 f2e8d6c772c0        3 weeks ago         324.6 MB
httpd               latest              02ef73cf1bc0        3 weeks ago         194.4 MB
ubuntu              15.10               4e3b13c8a266        5 weeks ago         136.3 MB
hello-world         latest              690ed74de00f        6 months ago        960 B
centos              6.7                 d95b5ca17cc3        6 months ago        190.6 MB
training/webapp     latest              6fae60ef3446        12 months ago       348.8 MB

Docker Image Usage