Docker Container Learning

Fri, Mar 20, 2020 7:27 PM

What is Docker ?

Docker is basically a container engine which uses the Linux Kernel features like namespaces and control groups to create containers on top of an operating system and automates application deployment on the container. Docker uses Copy-on-write union file system for its backend storage.

What is container ?

A Docker container is an open source software development platform. Its main benefit is to package applications in containers, allowing them to be portable to any system running a Linux or Windows operating system (OS). A Windows machine can run Linux containers by using a virtual machine (VM).

How to Docker?

Here are some basic things like how to install docker and how to we can pull images,build custom image, run containers,remove containers and see the logs, attach volume,inspect the config, etc…

Install Docker on fedora 31

Add Docker repository:

sudo dnf config-manager --add-repo=https://download.docker.com/linux/fedora/docker-ce.repo

Install docker

sudo dnf install docker-ce

Enable and Start Docker deamon.

sudo systemctl enable docker
sudo systemctl start docker

Search for Docker images

Search images from registry

​[snandago@sureshn ~]$ docker search http
NAME                                 DESCRIPTION                                     STARS               OFFICIAL            AUTOMATED
httpd                                The Apache HTTP Server Project                  2913                [OK]                
haproxy                              HAProxy - The Reliable, High Performance TCP…   1383                [OK]                
steveltn/https-portal                A fully automated HTTPS server powered by Ng…   88                                      [OK]
kennethreitz/httpbin                 A simple HTTP service.                          50                                      [OK]
centos/httpd-24-centos7              Platform for running Apache httpd 2.4 or bui…   31                                      
hashicorp/http-echo                  http-echo is an in-memory web server that ec…   26                                      
geldim/https-redirect                Very small http to https redirector based on…   17                                      [OK]
citizenstig/httpbin                  Docker container for httpbin: HTTP Request &…   14                                      [OK]
clue/httpie                          HTTPie is a cURL-like tool for humans. Usefu…   13                                      [OK]
alpine/httpie                        Auto-trigger docker build for `httpie` when …   10                                      [OK]
mendhak/http-https-echo              Listens on http/https, echoes details about …   8                                       [OK]
mainflux/http                        HTTP adapter service for Mainflux IoT platfo…   3                                       

Pull docker image from registry

using docker pull command we can pull the images locally

[snandago@sureshn ~]$ docker pull httpd
Using default tag: latest
latest: Pulling from library/httpd
68ced04f60ab: Pull complete 
35d35f1e0dc9: Pull complete 
8a918bf0ae55: Pull complete 
d7b9f2dbc195: Pull complete 
d56c468bde81: Pull complete 
Digest: sha256:946c54069130dbf136903fe658fe7d113bd8db8004de31282e20b262a3e106fb
Status: Downloaded newer image for httpd:latest
docker.io/library/httpd:latest
[snandago@sureshn ~]$

List locally Downloaded Docker images

docker images command shows the locally builded/downloaed images.

[snandago@sureshn ~]$ docker images 
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
myutil/httpd        latest              c8811902f987        57 minutes ago      381MB
httpd               latest              c5a012f9cf45        3 weeks ago         165MB
centos              latest              470671670cac        2 months ago        237MB
centos              latest              49f7960eb7e4        21 months ago       200MB
fedora/firefox      latest              7fa9c2fade45        3 years ago         880MB
[snandago@sureshn ~]$ 

Remove the Docker images

Remove docker images from local cab be done by docker rmi imagename

[snandago@sureshn ~]$ docker rmi httpd
Untagged: httpd:latest
Untagged: httpd@sha256:946c54069130dbf136903fe658fe7d113bd8db8004de31282e20b262a3e106fb
Deleted: sha256:c5a012f9cf45ce0634f5686cfb91009113199589bd39b683242952f82cf1cec1
Deleted: sha256:0f29a08770415263e178a4fd0114fe05e6dcc7d0c7922d5ee5430ad29dde9aef
Deleted: sha256:7e07c23416eb19df1444ae11062dc553d9e8eb8fd91f866b2ad2aa22954597b9
Deleted: sha256:997f97a68088ee2a31925e6deefcc690d8b45f2d795a5ce540e4d540d838fca7
Deleted: sha256:c61f156b49aa9f766f67b79ee6d7df6e83a4a2a0bda8da0c5ff19b3ea480cbd3
Deleted: sha256:f2cb0ecef392f2a630fa1205b874ab2e2aedf96de04d0b8838e4e728e28142da
[snandago@sureshn ~]$ 

Run container

Run container by docker run commands with Arguments required.

​[snandago@sureshn ~]$ docker run --name test_http -d -p 9090:80 httpd
cc80d4595d4c566af398b0ca145f7e9f82661e1751e397b59bdca3fd4a2b499e
[snandago@sureshn ~]$ 

Above docker command ran the test_http apcahe container with argument -d -p where -d make sure its run on backgroud and -p to expose port 80,we can verify it using curl localhost:9090 and Good news is it works!

[snandago@sureshn ~]$ curl 127.0.0.1:9090
<html><body><h1>It works!</h1></body></html>
[snandago@sureshn ~]$ 

Copy the file to running container

docker cp command can be used to copy the file to running container.

this below example show command to copy the index.html to running container path /var/www/html

[snandago@sureshn my_utils]$ docker cp index.html test-myutil:/var/www/html

List Running & Stopped Containers

Running containers can be listed using docker ps
docker ps only so the running container we can use -a argument to see all the containers [running|stopped]

[snandago@sureshn ~]$ docker ps 
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                  NAMES
cc80d4595d4c        httpd               "httpd-foreground"       6 minutes ago       Up 6 minutes        0.0.0.0:9090->80/tcp   test_http
2e8264b4050c        myutil/httpd        "/usr/sbin/httpd -D …"   27 minutes ago      Up 27 minutes       0.0.0.0:8081->80/tcp   test-myutil
[snandago@sureshn ~]$ 

[snandago@sureshn ~]$ docker ps -a
CONTAINER ID        IMAGE               COMMAND                  CREATED              STATUS                     PORTS                  NAMES
1da62939c4a4        httpd               "httpd-foreground"       15 seconds ago       Exited (0) 8 seconds ago                          stopped
6664c9d1bcf7        httpd               "httpd-foreground"       About a minute ago   Created                                           test_http2
cc80d4595d4c        httpd               "httpd-foreground"       9 minutes ago        Up 9 minutes               0.0.0.0:9090->80/tcp   test_http
2e8264b4050c        myutil/httpd        "/usr/sbin/httpd -D …"   30 minutes ago       Up 30 minutes              0.0.0.0:8081->80/tcp   test-myutil
[snandago@sureshn ~]$ 

Kill the Running Containers

Kill the running container using docker kill command

[snandago@sureshn ~]$ docker kill test_http
test_http
[snandago@sureshn ~]$ 

Remove the Containers

docker rm command can be used to remove container

If you would like to remove multiple containers at on shot just run docker rm $(docker ps -a -q)

[snandago@sureshn ~]$ docker rm test_http
test_http
[snandago@sureshn ~]$ 

Run commands on Running Container

Using docker exec command we can Run a command in a running container

[snandago@sureshn ~]$ docker exec httpd_test ls /var/log
alternatives.log
apt
btmp
dpkg.log
faillog
lastlog
wtmp
[snandago@sureshn ~]$ docker exec httpd_test date
Fri Mar 20 12:42:06 UTC 2020
[snandago@sureshn ~]$
[snandago@sureshn ~]$ docker exec httpd_test env
PATH=/usr/local/apache2/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=622b2f999cd2
HTTPD_PREFIX=/usr/local/apache2
HTTPD_VERSION=2.4.41
HTTPD_SHA256=133d48298fe5315ae9366a0ec66282fa4040efa5d566174481077ade7d18ea40
HTTPD_PATCHES=
HOME=/root
[snandago@sureshn ~]$

ssh container

Using docker exec -it and /bin/bash conainer name we can ssh into container.

[snandago@sureshn search_index]$ docker exec -it grafana /bin/bash 
bash-5.0$ grafana-cli -v
Grafana CLI version 6.7.1
bash-5.0$ 

Add storage to the Container

by adding VOLUME in docker file we can attach the storage

docker -v path:containerpath will attach the persistance storage to the container.

[snandago@sureshn docker]$ docker run --name con_volume_test -v /home/snandago/learning/docker:/var/www/html -d -p 9010:80 centos/httpd
dd126bb53c2f5f427b92997a6a51181f638d0aa05bf0d76c6fd9a3d1a47911ba
[snandago@sureshn docker]$ docker exec con_volume_test df
Filesystem                                            1K-blocks      Used Available Use% Mounted on
overlay                                               103077688  52877616  44940812  55% /
tmpfs                                                     65536         0     65536   0% /dev
shm                                                       65536         0     65536   0% /dev/shm
/dev/mapper/luks-66ddcfec-d738-46c9-ab1d-3954bf254999 103077688  52877616  44940812  55% /etc/hosts
/dev/mapper/luks-841e521e-de10-4ae5-9e7d-d76dac326fa7 367219400 204250500 144292064  59% /var/www/html
tmpfs                                                   9943936         0   9943936   0% /proc/asound
tmpfs                                                   9943936         0   9943936   0% /proc/acpi
tmpfs                                                   9943936         0   9943936   0% /proc/scsi
tmpfs                                                   9943936         0   9943936   0% /sys/firmware
[snandago@sureshn docker]$ docker exec con_volume_test ls -l /var/www/html
total 4
-rw-rw-r--. 1 1000 1000 84 Mar 20 12:57 index.html
[snandago@sureshn docker]$ curl 127.0.0.1:9010
<html> 

<body>

<b> Test file volume attached to container. </b>

</body>

</html>
[snandago@sureshn docker]$ 

Inspect the Container configs

docker inspect command show provides detailed information on constructs controlled by Docker.

[snandago@sureshn ~]$ docker inspect -f '{{ .NetworkSettings.IPAddress }}' test-myutil
172.17.0.2
[snandago@sureshn ~]$ 

[snandago@sureshn ~]$ docker inspect --format='{{range .NetworkSettings.Networks}}{{.MacAddress}}{{end}}'  test-myutil
02:42:ac:11:00:02
[snandago@sureshn ~]$ 

Above docker inspect filter show container ip address and next filter show mac address. We can can filter multiple informations.

Build Custom image

by writing the Dockerfile we can build the custome image by our wish.

below is the sample Dockerfile

[snandago@sureshn docker]$ cat Dockerfile 
#sample Dockerfile
FROM centos
 
MAINTAINER [e-mail]

RUN yum install -y httpd; yum clean all

COPY index.html /var/www/html

EXPOSE 80

CMD ["/usr/sbin/httpd", "-D", "FOREGROUND"]
[snandago@sureshn docker]$ 

Small explaination on Dockerfile writing. How this file wrting is done.

Dockerfile file must start with FROM instruction we can add the base image name there.

The MAINTAINER instruction allows you to set the Author field of the generated images.

RUN <command> (shell form, the command is run in a shell, which by default is /bin/sh -c on Linux or cmd /S /C on Windows)

COPY Copies new files or directories from <src> and adds them to the filesystem of the image at the path <dest>.

EXPOSE Informs Docker that the container listens on the specified network port(s) at runtime.

CMD The main purpose of a CMD is to provide defaults for an executing container. These defaults can include an executable, or they can omit the executable, in which case you must specify an ENTRYPOINT instruction as well.

create a Dockerfile and run docker build command to build the custom image.

[snandago@sureshn docker]$ docker build -t custombuild_image .
Sending build context to Docker daemon  3.072kB
Step 1/6 : FROM centos
 ---> 470671670cac
Step 2/6 : MAINTAINER [e-mail]
 ---> Running in dfb3416849c6
Removing intermediate container dfb3416849c6
 ---> 03af3fb70aad
Step 3/6 : RUN yum install -y httpd; yum clean all
 ---> Running in ae9595d0dede
CentOS-8 - AppStream                            1.9 MB/s | 6.5 MB     00:03    
CentOS-8 - Base                                 2.6 MB/s | 5.0 MB     00:01    
CentOS-8 - Extras                               5.7 kB/s | 4.2 kB     00:00    
Dependencies resolved.
================================================================================
 Package           Arch   Version                               Repo       Size
================================================================================
Installing:
 httpd             x86_64 2.4.37-16.module_el8.1.0+256+ae790463 AppStream 1.7 M
Installing dependencies:
 apr               x86_64 1.6.3-9.el8                           AppStream 125 k
 apr-util          x86_64 1.6.1-6.el8                           AppStream 105 k
 centos-logos-httpd
                   noarch 80.5-2.el8                            AppStream  24 k
 httpd-filesystem  noarch 2.4.37-16.module_el8.1.0+256+ae790463 AppStream  35 k
 httpd-tools       x86_64 2.4.37-16.module_el8.1.0+256+ae790463 AppStream 103 k
 mod_http2         x86_64 1.11.3-3.module_el8.1.0+213+acce2796  AppStream 158 k
 brotli            x86_64 1.0.6-1.el8                           BaseOS    323 k
 mailcap           noarch 2.1.48-3.el8                          BaseOS     39 k
Installing weak dependencies:
 apr-util-bdb      x86_64 1.6.1-6.el8                           AppStream  25 k
 apr-util-openssl  x86_64 1.6.1-6.el8                           AppStream  27 k
Enabling module streams:
 httpd                    2.4                                                  

Transaction Summary
================================================================================
Install  11 Packages

________trimmed some content to make it smaller-----------------------------
Complete!
20 files removed
Removing intermediate container ae9595d0dede
 ---> 1e797d9d4344
Step 4/6 : COPY index.html /var/www/html
 ---> f6b8f7331d0e
Step 5/6 : EXPOSE 80
 ---> Running in 1c0f40e48936
Removing intermediate container 1c0f40e48936
 ---> 878e8361d5ce
Step 6/6 : CMD ["/usr/sbin/httpd", "-D", "FOREGROUND"]
 ---> Running in 5d8785e85068
Removing intermediate container 5d8785e85068
 ---> d0ee1706467b
Successfully built d0ee1706467b
Successfully tagged custombuild_image:latest
[snandago@sureshn docker]$ 

docker images show up the custom buid image. Now we can try running this container.

[snandago@sureshn docker]$ docker images 
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
custombuild_image   latest              d0ee1706467b        5 minutes ago       259MB
myutil/httpd        latest              c8811902f987        2 hours ago         381MB
centos              latest              470671670cac        2 months ago        237MB
centos/httpd        latest              2cc07fbb5000        14 months ago       258MB
centos              latest              49f7960eb7e4        21 months ago       200MB
fedora/firefox      latest              7fa9c2fade45        3 years ago         880MB
[snandago@sureshn docker]$ docker run --name custom_build -d -p 9098:80 custombuild_image
39c1ac7a24067e5030a214c96c0cc58cca0ca11dfd22646b78d29e2daabb1dce
[snandago@sureshn docker]$ curl 127.0.0.1:9098
Cutom build tested!
[snandago@sureshn docker]$ 

yes! we can see the container running and the index.html file we copied while build shows up.

Running mysql container

Run the mysql container mysql-57-centos7 docker registry image.

docker run -d --name mysql \
-v /mydata/data:/var/lib/mysql/init \
-e MYSQL_DATABASE=lab \
-e MYSQL_USER=user \
-e MYSQL_PASSWORD=password \
-e MYSQL_ROOT_PASSWORD=password! \
centos/mysql-57-centos7

find the network details of the container and connect the db and verify.

docker inspect -f '{{ .NetworkSettings.IPAddress }}' mysql

[snandago@sureshn data]$ mysql -u root -p -h 172.17.0.2
Enter password: 
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MySQL connection id is 38
Server version: 5.7.24 MySQL Community Server (GPL)

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MySQL [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| lab                |
| mysql              |
| new_schema         |
| performance_schema |
| sys                |
+--------------------+
6 rows in set (0.002 sec)

MySQL [(none)]> use lab;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
MySQL [lab]> show tables;
+---------------+
| Tables_in_lab |
+---------------+
| data          |
| lab_inventory |
+---------------+
2 rows in set (0.001 sec)

MySQL [lab]> 

tags: container docker Learning