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Saturday, April 6, 2019

Configure Secure Docker Registry with Docker-Distribution

Configure Secure Registry with Docker-Distribution on CentOS 7

Docker Registry is a content storage and delivery system, that stores different tagged versions of Docker images. Users interact with the Registry by means of a Push or Pull methods. Docker Hub is a public docker registry that provides millions of images to trillions of users. But there are scenarios, where we are required to setup a private and secure in-premises Docker Registry.

We have already configured a Private Docker Registry on CentOS 7 in our previous article by using containers technology, where we have created a Registry container by using Docker Engine CE.

Now, we are using an alternate method to create a Secure Docker Registry without using containers. In this article, we will configure a Secure Registry with Docker-Distribution on CentOS 7 and then test it by using it through Docker hosts.

It is highly recommended that you should read Docker Deep Dive for some basic to advance level understanding of Docker technology. It will also help you to better understand this article.

Configure Secure Registry with Docker-Distribution on CentOS 7

Table of Contents:


System Specification:

We have configured a CentOS 7 virtual machine with following specification.

  • Hostname - dregistry-01.centlinux.com
  • IP Address -
  • Operating System - CentOS 7.6
  • CPU - 3.4 Ghz (1 Core)
  • Memory - 1 GB
  • Storage - 40 GB

We are also using a Docker Host with following specification to test our Secure Docker Registry.

  • Hostname - docker-manager-01.centlinux.com
  • IP Address -
  • Operating System - CentOS 7.6
  • Docker Version - Docker Engine CE 18.09


Installing Docker-Distribution on CentOS 7:

Connect with dregistry-01.centlinux.com using ssh as root user.

Docker-Distribution package is available in extras yum repository.

Check the available version of Docker-Distribution package.

# yum info docker-distribution
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: mirrors.ges.net.pk
 * extras: mirrors.ges.net.pk
 * updates: mirror1.ku.ac.th
Installed Packages
Name        : docker-distribution
Arch        : x86_64
Version     : 2.6.2
Release     : 2.git48294d9.el7
Size        : 12 M
Repo        : installed
From repo   : extras
Summary     : Docker toolset to pack, ship, store, and deliver content
URL         : https://github.com/docker/distribution
License     : ASL 2.0
Description : Docker toolset to pack, ship, store, and deliver content

Install above package with the help of yum command.

# yum install -y docker-distribution


Configuring Secure Registry with Docker-Distribution:

We are configuring a Secure Docker Registry, therefore, we have to create a SSL/TLS certificate for it.

# openssl req \
> -newkey rsa:2048 \
> -nodes -sha256 \
> -x509 -days 365 \
> -keyout /etc/pki/tls/private/registry.key \
> -out /etc/pki/tls/registry.crt
Generating a 2048 bit RSA private key
writing new private key to '/etc/pki/tls/private/registry.key'
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
Country Name (2 letter code) [XX]:PK
State or Province Name (full name) []:Sindh
Locality Name (eg, city) [Default City]:Karachi
Organization Name (eg, company) [Default Company Ltd]:Ahmer's SysAdmin Recipes
Organizational Unit Name (eg, section) []:ITLAB
Common Name (eg, your name or your server's hostname) []:dregistry-01.centlinux.com
Email Address []:root@dregistry-01.centlinux.com

To restrict anonymous access, we will setup basic HTTP authentication for our Docker Registry Service. For this purpose, we need to install htpasswd utility to create a HTTP password file.

# yum install -y httpd-tools

Now, create a HTTP password file as follows:

# htpasswd -c -B /etc/docker-distribution/dockerpasswd ahmer
New password:
Re-type new password:
Adding password for user ahmer

We have used -B switch above to create an entry with bcrypt encryption because it is the only supported format right now, and the entries with other hash types will be ignored.

Edit config.yml configuration file in vim text editor.

# vi /etc/docker-distribution/registry/config.yml

and update it as follows:

version: 0.1
    service: registry
        layerinfo: inmemory
        rootdirectory: /var/lib/registry
        certificate: /etc/pki/tls/registry.crt
        key: /etc/pki/tls/private/registry.key
        realm: centlinux.com
        path: /etc/docker-distribution/dockerpasswd

Warning: Avoid use of TAB key for indention of lines. Otherwise, the service will give you following error during startup.

configuration error: error parsing /etc/docker-distribution/registry/config.yml: yaml: line 12: found character that cannot start any token

Please refer to Docker Documentation for more configuration options in config.yml.

Start and Enable Secure Registry service.

# systemctl start docker-distribution
# systemctl enable docker-distribution

Allow Docker Registry service port 5000/tcp in Linux Firewall.

# firewall-cmd --permanent --add-port=5000/tcp
# firewall-cmd --reload

Use Secured Docker Registry on Docker Hosts:

Connect with Docker Host (docker-manager-01.centlinux.com) by using ssh as root user.

Add an entry in Local DNS Resolver to setup name resolution of our Secure Registry Server.

# cat >> /etc/hosts << EOF
> dregistry-01.centlinux.com dregistry-01

Install Registry Service TLS/SSL certificate on Docker Host.

# mkdir -p /etc/docker/certs.d/dregistry-01.centlinux.com:5000
# scp root@dregistry-01:/etc/pki/tls/registry.crt /etc/docker/certs.d/dregistry-01.centlinux.com\:5000/
root@dregistry-01's password:

Pull an image from Docker Hub. We will later push this image into our Secure Docker Registry.

# docker pull alpine
Using default tag: latest
latest: Pulling from library/alpine
8e402f1a9c57: Pull complete
Digest: sha256:644fcb1a676b5165371437feaa922943aaf7afcfa8bfee4472f6860aad1ef2a0
Status: Downloaded newer image for alpine:latest

Tag alpine image before pushing it to Secure Docker Registry.

# docker tag alpine dregistry-01.centlinux.com:5000/alpine

Login to Secure Registry.

# docker login dregistry-01.centlinux.com:5000
Username: ahmer
WARNING! Your password will be stored unencrypted in /root/.docker/config.json.
Configure a credential helper to remove this warning. See

Login Succeeded

Push alpine image to our Secure Docker Registry.

# docker push dregistry-01.centlinux.com:5000/alpine
The push refers to repository [dregistry-01.centlinux.com:5000/alpine]
bcf2f368fe23: Pushed
latest: digest: sha256:d05ecd4520cab5d9e5d877595fb0532aadcd6c90f4bbc837bc11679f704c4c82 size: 528

We have Successfully configured a Secure Registry with Docker-Distribution on CentOS 7.

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