The size of the Docker Image was suddenly increasing, I will check it. Using docker history <Image name> you can check the change history for Image before. Now, let’s Docker Images history.

Docker Images history

Docker pull command

Requires Image to be downloaded locally. As an example, I use docker pull image centos as below

[vagrant@localhost ~]$ docker pull centos:6.10
6.10: Pulling from library/centos
1c8f9aa56c90: Pull complete
Digest: sha256:b4c3fe75b135ca1c26ef6feb8153aade8a31c4e3e763376529c1088de7e973f4
Status: Downloaded newer image for centos:6.10

[vagrant@localhost ~]$ docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
centos              6.10                30e66b619e9f        4 months ago        194MB

Try it

The output order is new, and it seems that it becomes an old layer as going down as below

[vagrant@localhost ~]$ docker history centos:6.10
IMAGE               CREATED             CREATED BY                                      SIZE                COMMENT
30e66b619e9f        4 months ago        /bin/sh -c #(nop)  CMD ["/bin/bash"]            0B
<missing>           4 months ago        /bin/sh -c #(nop)  LABEL org.label-schema.sc…   0B
<missing>           4 months ago        /bin/sh -c #(nop) ADD file:769078df784180af4…   194MB

Also, With the “–human” option, the actual date is displayed below

[vagrant@localhost ~]$ docker history centos:6.10 --human=false
IMAGE               CREATED AT                  CREATED BY                                      SIZE                COMMENT
30e66b619e9f        2018-10-10T01:22:51+07:00   /bin/sh -c #(nop)  CMD ["/bin/bash"]            0
<missing>           2018-10-10T01:22:51+07:00   /bin/sh -c #(nop)  LABEL org.label-schema.sc…   0
<missing>           2018-10-10T01:22:51+07:00   /bin/sh -c #(nop) ADD file:769078df784180af4…   193889316

Docker inspect container information

Using docker inspect command to Confirmation of container information.

[vagrant@localhost ~]$ docker inspect centos:6.10
[
    {
        "Id": "sha256:30e66b619e9f73941f418bb08a081132607433f5b8ccaefd3b7bceb08c770b20",
        "RepoTags": [
            "centos:6.10"
        ],
        "RepoDigests": [
            "centos@sha256:b4c3fe75b135ca1c26ef6feb8153aade8a31c4e3e763376529c1088de7e973f4"
        ],
        "Parent": "",
        "Comment": "",
        "Created": "2018-10-09T18:22:51.586650744Z",
        "Container": "9a31860c3402344acd1f16127fec864b93038c86e8716f08e5dc2a60851a602e",
        "ContainerConfig": {
            "Hostname": "9a31860c3402",
            "Domainname": "",
            "User": "",
            "AttachStdin": false,
            "AttachStdout": false,
            "AttachStderr": false,
            "Tty": false,
            "OpenStdin": false,
            "StdinOnce": false,
            "Env": [
                "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
            ],
            "Cmd": [
                "/bin/sh",
                "-c",
                "#(nop) ",
                "CMD [\"/bin/bash\"]"
            ],
            "ArgsEscaped": true,
            "Image": "sha256:34321cccc68dac29b496363ca05c47e7f23c3e59d664fea4de03695975443b8b",
            "Volumes": null,
            "WorkingDir": "",
            "Entrypoint": null,
            "OnBuild": null,
            "Labels": {
                "org.label-schema.build-date": "20180804",
                "org.label-schema.license": "GPLv2",
                "org.label-schema.name": "CentOS Base Image",
                "org.label-schema.schema-version": "1.0",
                "org.label-schema.vendor": "CentOS"
            }
        },
        "DockerVersion": "17.06.2-ce",
        "Author": "",
        "Config": {
            "Hostname": "",
            "Domainname": "",
            "User": "",
            "AttachStdin": false,
            "AttachStdout": false,
            "AttachStderr": false,
            "Tty": false,
            "OpenStdin": false,
            "StdinOnce": false,
            "Env": [
                "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
            ],
            "Cmd": [
                "/bin/bash"
            ],
            "ArgsEscaped": true,
            "Image": "sha256:34321cccc68dac29b496363ca05c47e7f23c3e59d664fea4de03695975443b8b",
            "Volumes": null,
            "WorkingDir": "",
            "Entrypoint": null,
            "OnBuild": null,
            "Labels": {
                "org.label-schema.build-date": "20180804",
                "org.label-schema.license": "GPLv2",
                "org.label-schema.name": "CentOS Base Image",
                "org.label-schema.schema-version": "1.0",
                "org.label-schema.vendor": "CentOS"
            }
        },
        "Architecture": "amd64",
        "Os": "linux",
        "Size": 193889316,
        "VirtualSize": 193889316,
        "GraphDriver": {
            "Data": {
                "MergedDir": "/var/lib/docker/overlay2/f799911e2d9e2de958ee359b6a6e125a93a69992c34851acb63ec1f22e2f9da2/merged",
                "UpperDir": "/var/lib/docker/overlay2/f799911e2d9e2de958ee359b6a6e125a93a69992c34851acb63ec1f22e2f9da2/diff",
                "WorkDir": "/var/lib/docker/overlay2/f799911e2d9e2de958ee359b6a6e125a93a69992c34851acb63ec1f22e2f9da2/work"
            },
            "Name": "overlay2"
        },
        "RootFS": {
            "Type": "layers",
            "Layers": [
                "sha256:18c81886066a186e754291bab5ae87b273b274c66c2c9fea8e869a7cb67dac1b"
            ]
        },
        "Metadata": {
            "LastTagTime": "0001-01-01T00:00:00Z"
        }
    }
]

Extract only environment variables as below

[vagrant@localhost ~]$ docker inspect --format='{{range .Config.Env}}{{println .}}{{end}}' centos:6.10
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

Conclusion

Through the article, You can inspect “Docker images history” as above. I hope will this your helpful. Thank you for reading the DevopsRoles page!

Introduction

In this tutorial, I use Nginx reverse proxy for Jenkins in docker as the whole picture below

Procedure as below

• Host OS: Install Nginx and Docker. Using account root for setup server.
• Docker containers: Jenkins and app_devops

Installing and Configuring on CentOS/RedHat 7/6

Install Epel and Remi repository on CentOS/RedHat 6/7

### Install Epel For CentOS/RHEL 7 ###
# rpm -Uvh http://dl.fedoraproject.org/pub/epel/7/x86_64/Packages/e/epel-release-7-11.noarch.rpm

### Install Epel For CentOS/RHEL 6 ###
# rpm -Uvh http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm

### Install REMI Repository For CentOS/RHEL 7 ###
rpm -Uvh http://rpms.famillecollet.com/enterprise/remi-release-7.rpm

### Install REMI Repository For CentOS/RHEL 6 ###
rpm -Uvh http://rpms.famillecollet.com/enterprise/remi-release-6.rpm

Docker install

Install docker and learn containers on Centos

See more

Nginx install

# yum install nginx

start Nginx service

# service nginx start

Set up Jenkins with docker

Set up Jenkins with docker

See more

Nginx configure

Creating Nginx configuration file directory for myapp

# mkdir /etc/nginx/conf.d/myapp/

Backup the default configuration file

# mv /etc/nginx/conf.d/default.conf  /etc/nginx/conf.d/default.conf_bk

Create the configuration file for myapp

# vi /etc/nginx/conf.d/server.conf

The content is below

server {
    listen       80;
    include /etc/nginx/default.d/*.conf;
    root         /usr/share/nginx/html;
    #common
    proxy_set_header    Host $host:$server_port;
    proxy_set_header    X-Real-IP    $remote_addr;
    proxy_set_header    X-Forwarded-Host       $host:$server_port;
    proxy_set_header    X-Forwarded-Server    $host:$server_port;
    proxy_set_header    X-Forwarded-For    $proxy_add_x_forwarded_for;
    proxy_set_header    X-Forwarded-Proto $scheme;

    include /etc/nginx/conf.d/myapp/*.conf;
}

Nginx reverse proxy for devopsroles.com and jenkins Configuring

Creating file devops.conf in folder myall

# vi /etc/nginx/conf.d/myapp/devops.conf

The content is below

#for myapp
location /devopsroles/ {
    proxy_pass    http://localhost:68081/;
    proxy_redirect  http://localhost:68081/ /devopsroles/;

}

# For jenkins
location /dev_jenkins/ {
    proxy_pass    http://localhost:68080 ;
    proxy_redirect  http://localhost:68080/ /dev_jenkins/;
}

Conclusion

Through the article, You can set up “ Nginx reverse proxy for Jenkins in docker“ as above. I hope will this your helpful. Thank you for reading the DevopsRoles page!

In this article, I will write about “data mount (volume), Docker Network, Docker Compose”. Now, let’s go Docker tutorial series – part 2.

Data management in Docker

Dynamic data to be handled in the started container can be placed in the top layer (container layer) that can be read and written.

• When the container is deleted, data in the container disappears.
• Can not share data among containers.
• Since writing to the container layer uses a union file system different from the normal file system, the writing speed is slow.

Disadvantage

Docker manages data on the host machine and mounts it on the container is used.

There are three main methods, which I will explain below.

volume

A method of mounting the specified directory (/var/lib/docker/volumes) which is automatically generated on the host machine to the container

On the host machine

$ docker volume create [volume name]

By doing so, When you create a volume (/var/lib/docker/volumes directory) and start up the container.

For example
$ docker run -itd -name mount-test --mount source=volume1,target=/app nginx

You can mount the specified volume by attaching the –mount option (it can also be the -v option) as shown in.

The mounted volumes directory should not be directly manipulated from the directory on the host from which it is mounted.

Even different containers that are set up on the same host can share files by mounting the same volume respectively.

Furthermore, if you want to share volume with multiple containers, you can also set edit permission for each container.

$ docker run -itd -name mount-c4 --mount source=copy-vol,destination=/etc/nginx,readonly nginx

volume management command

Check volume list

$ docker volume ls

Check volume details

$ docker volume inspect [volume name]

Delete volume

$ docker volume rm [volume name]

Note that deleting the container will keep the volume, so you need to delete it with the $docker volume rm [volume name].

bind mount

Bind mount is a mount method different from the volume, in that you can mount arbitrary directories on the host machine and directly manipulate directories on the host side.

It is not necessary to set it in advance like volume, but mount it by specifying it as an option at container startup with the following command.

For example:
$ docker run -itd -name bind-mount-test --mount type=bind,source="$ (pwd)"/mount,target=/app nginx

If the source (mount source) directory does not exist, an error will occur, so let’s make it in advance. (It is automatically created when using the -v option)

if you mount an empty directory on the host. on the container, data on the container will disappear and the container may not work properly, so be careful.

tmpfs (tempfs)

A method of mounting the memory area of the host machine on the container

Whether the host machine is terminated or when the container is closed, the held data is released.

For example:
$ docker run --itd --name tmpfs-test --mount type=tmpfs,destination=/app nginx

You can mount by specifying as the type of the -mount option at the time of container startup.

Also, in order to eliminate the possibility of unlimited use of memory on the host,

$ docker run --itd --name tmpfs-test --mount type=tmpfs,destination=/app,tmpfs-size=100000000,tmpfs-mode=800 nginx

You can also limit the memory size that can be used as an option.

Docker network

we will explain here the method of communicating between multiple containers launched.

For example, when operating a web page, if you start up a WordPress container and a MySQL container, the WordPress container needs to communicate with the MySQL container.

As a method of inter-container communication here, it is the Docker network that connects and communicates with multiple containers.

The Docker network has three networks that exist by default and networks that you define yourself.

Bridge network

In the existing network by default, the created container is connected by default to the bridge network.

In the Bridge network, you can communicate with a container that exists in the same network by specifying an IP address.
However, in the Bridge network, since DNS is not defined, the container name can no communicate with other containers.

In other words, it is possible to communicate by specifying an IP address among containers launched without specifying Network, but it is impossible to communicate by specifying a container name.

Although it is a network that is not exposed to the outside in the default state, it can be accessed from the outside by releasing the port specified by the -p option.

Host network

The host network is the network that exists by default with the host driver.

The connected container will have the same network settings as the docker host.

Therefore, it is possible to connect to the container by connecting to the Docker host’s IP number 80 only by starting the container without setting the -p option at the container startup and opening the port to the outside like the bridge network I will.

None Network

It is the default existing network, and the connected container has no network interface. When connecting to a network, it is necessary to be disconnected from all other networks.

Docker create

By creating your own network, you can communicate between containers by container name.

$ docker network create [network name]

Create a new network with (Default driver is a bridge)

$ docker network connect [Network name to connect to] [Container name]

Docker Daemon’s built-in DNS works on the user-defined unique network resolve names by container name and associates with IP, so you can connect to other containers by container name.

Network commands

Check the network list

$ docker network ls

Check network details

$ docker network inspect [network name]

Create a new network

$ docker network create [network name]

The default driver is bridge

Connect a container to a network

$ docker network connect[ Network name to connect to] [Container name]

Disconnect container from a network

$ docker network disconnect Network name container name

Docker Compose

Docker Compose is a tool for predefining and running multiple container Docker applications. So, Docker Compose is able to automate them.

When building the execution environment of a Web service with Docker, by writing the definitions of the Web server, DB server, Cache server, etc. in one docker-compose.yml file, based on that, the container required for execution You can start and set all at once.

The procedure is as follows.

• Prepare a Dockerfile or prepare an image to use for Docker Hub etc.
• Define docker-compose.yml
• Execute $ docker-compose up in the directory containing the yml file

docker-compose command list

Display a list of containers started with docker-compose

$ docker-compose ps

Container activation from the setting described in docker-compose.yml

$ docker-compose up

It restarts even if the container is already running

Delete containers and networks created with docker-compose

$ docker-compose down
# $ docker-compose down -v

The volume is also deleted together with the -v option

Execute command within specified service container

$ docker-compose run [container name] [command]

A series of container stops

$ docker-compose stop

A series of container activation

$ docker-compose start

Docker tutorial series – part 1

In this article, I will Write about understanding the mechanism of Docker. The whole picture of various concepts around Docker. Now, let’s go Docker tutorial series part 1.

docker-compose
docker-machine
docker swarm, etc. from the basics of images and containers.

In the Docker tutorial series part 1

I will write about “the container, image, image sharing with DockerHub“.

What is Docker

It is “container type virtualization technology” provided by Docker.

What is Virtualization?

• “Virtual computer in PC or Server” is virtualization.
• Host operating system installed on a machine such as PC or server.
• Hosted virtualization uses a virtualization software/hypervisor on a Host OS to launch a Virual Machine call is Guest OS

Container type virtualization?

• Docker provides container type virtualization.
• Containers are build from Docker Engine running on Host OS without booting guest OS.

Docker Engine

Docker Engine will operate as a resident program and you can use Docker.

Tag

The Docker image has the concept of tag. Tag is the “version of image”. If no tag name is specified, the “latest” tag is automatically used.

For example, the image name and tag name as below

nginx: latest
nginx: 1.14-wordpress

image structure

• it has a layer structure
• Once created image is not editable (read only)

The layer of the image is Read-only, it can not be edited, only the container layer created when the container is activated from an image can be edited.

List image on the local machine as command below

$ docker images

How to prepare image

• Obtain an image made by others (mainly from Docker Hub)
• Make it yourself

I will go through step by step

1. Image from Docker Hub

Retrieve image from #dockerhub (server hosted by docker)

$ docker pull <image name>

2. Image creation from Dockerfile

Create a text file named Dockerfile, describe the settings related to image build (image creation) in it.

Dockerfile example

# CentOS 7 Dockerfile
 # Docker build:
 # sudo docker build -t devopsroles/centos:latest .
 # Docker create:
 # sudo docker create -it --name centos -h centos devopsroles/centos
 # Docker start:
 # sudo docker start centos
 # Connect with bash
 # sudo docker exec -it centos bash
 FROM centos:latest
 MAINTAINER PHAN VAN HUU <pvhuu90@gmail.com> My blogs: devopsroles.com
 #Update centos
 RUN yum update -y && yum upgrade -y
 RUN yum -y install git curl net-tools wget vim
 # Install EPEL Repository
 RUN yum install -y epel-release
 # Clean CentOS 7
 RUN yum clean all
 # Set the environment variables
 ENV HOME /root
 # Working directory
 WORKDIR /root
 # Default command
 CMD ["bash"]

Docker build the image from our Dockerfile

$ sudo docker create -it --name centos -h centos devopsroles/centos

Docker Container

After preparing the image, the container can be started from the image.

Launch container from image

Create containers from images as command below

$ docker create --name centos

As a command to acquire and start a container by acquiring the specified image that we have seen from DockerHub. Launch Container as command below

$ docker start <Container name>

The docker run command is the command to execute at the same time.

$ docker run <image name>

• Retrieve images from DockerHub : docker pull
• Create container from acquired image: docker create
• Start up the created container: docker start

Docker container commands

Show currently running Container

$ docker ps

Display container list currently existing

$ docker ps -a

Display detailed information of the container

$ docker inspect <container name>

Create Container

$ docker create --name <arbitrary name of container> -it <image name> /bin/bash

Launch Container with the command below

$ docker start <container name>

You can pause containers

$ docker pause <container name>

you can cancel the pause of the container with the command below

$ docker unpause <container name>

Restarting the container. If you do not use containers you do not use, your hard disk will be pressured.

$ docker stop <container name>

Delete Container

$ docker rm <container name>

Forced removal container

$ docker rm -f <container name>

Connect to the shell of the active container

There are two connection methods, using docker attach and docker exec

$ docker attach <Starting Container Name>
$ docker exec -it <Starting Container Name> /bin/bash

Create an image from a container

A command to save the state of the container as an image with the specified “<image name>: <tag name>“

$ docker commit <container name> <image name>:<tag name>

You can check the change history of the image

$ docker history <image name>

3. Docker Hub (Docker Registry)

Sharing images with Docker Hub

It is almost the same as Github. You need to have a Dockerhub account.

As a procedure

• Create repository on Docker hub
• Create image locally
• Log in to the docker hub with the following command on the local command line

$ docker login

4. Tag the image you want to push with the following command

$ docker tag <image name you want to push> <docker hub ID>/<image name>:<tag name>

5. Push the local image to the remote repository with the following command

$ docker push <docker hub ID>/<image name>:<tag name>

Docker tutorial series – part 2