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Build a Docker Private Registry with Self-Signed SSL

Recently I’ve been getting back into Kubernetes, which, for the time being, uses Docker as the underlying container CRUD system. At some point when using k8s one will likely need a private Docker registry.

Frankly the hardest part of this is getting the SSL certificates to work.

Assumptions

Create SSL Certificates

I’m not 100% sure of the model I’m using to create the SSL certificates, but it is working with Docker. I don’t know if you’d want to use it in production. :)

First, I create a OpenSSL configuration file called ca.conf. You might want to edit the distinguished name variables as well as the CN and alt_names.

[req]
distinguished_name = req_distinguished_name
req_extensions  = v3_req
x509_extensions = v3_ca
prompt = no
[req_distinguished_name]
C = CA
ST = Alberta
L = Edmonton
O = Example.com
OU = CA
CN = ca.example.com
[v3_req]
keyUsage = keyEncipherment, dataEncipherment, keyCertSign
extendedKeyUsage = serverAuth
subjectAltName = @alt_names
[ v3_ca ]
subjectKeyIdentifier=hash
authorityKeyIdentifier=keyid:always,issuer
basicConstraints = CA:true
[alt_names]
DNS.1 = ca.example.com

Next I also created a server.conf OpenSSL config file. You will want to change the CN and IP.1 or DNS.1. I am using an IP.

[req]
distinguished_name = req_distinguished_name
x509_extensions = v3_req
prompt = no
[req_distinguished_name]
C = CA
ST = Alberta
L = Edmonton
O = Example.com
OU = Docker
CN = registry.example.com
[v3_req]
keyUsage = keyEncipherment, dataEncipherment
extendedKeyUsage = serverAuth
subjectAltName = @alt_names
basicConstraints = CA:FALSE

[alt_names]
#DNS.1 = registry.example.com
IP.1 = <ip of registry server>

Now that we have those configured, we can run this script. Note that this will update the local CA repository and restart Docker.

#!/bin/bash

set -e

openssl genrsa -out ca-privkey.pem 2048
openssl req -config ./ca.conf -new -x509 -key ca-privkey.pem \
     -out cacert.pem -days 365
openssl req -config ./server.conf -newkey rsa:2048 -days 365 \
     -nodes -keyout server-key.pem -out server-req.pem
openssl rsa -in server-key.pem -out server-key.pem
openssl x509 -req -in server-req.pem -days 365 \
      -CA cacert.pem -CAkey ca-privkey.pem \
      -set_serial 01 -out server-cert.pem  \
      -extensions v3_req \
      -extfile server.conf

echo "INFO: print cacert.pem..."
openssl x509 -text -in cacert.pem -noout
echo "INFO: print server-req.pem..."
openssl req -text -in server-req.pem -noout
echo "INFO: print server-cert.pem..."
openssl x509 -text -in server-cert.pem -noout
openssl verify -verbose -CAfile ./cacert.pem server-cert.pem

echo "INFO: updating local CA..."

# Have to use .crt file name for update command to work
sudo cp cacert.pem /usr/local/share/ca-certificates/cacert.crt
sudo update-ca-certificates
echo "INFO: restarting docker"
sudo service docker restart

The cacert.pem file would need to be distributed to all hosts that would use the private repository.

Create a Docker registry

The Docker documentation has an example of doing this.

docker run -d -p 5000:5000 --restart=always --name registry \
  -v `pwd`/certs:/certs \
  -e REGISTRY_HTTP_TLS_CERTIFICATE=/certs/server-cert.pem \
  -e REGISTRY_HTTP_TLS_KEY=/certs/server-key.pem \
  registry:2

The above assumes the certs that were created with the ssl.sh script are in a certs directory.

Push an Image

Now that a docker registry is running, I can push an image to it, and have done so. I find the Docker tagging and pushing system very awkward.

$ docker images
REPOSITORY                    TAG                 IMAGE ID            CREATED             SIZE
10.70.0.28:5000/static-site   latest              fcaa5e0ee8f2        9 hours ago         109 MB
static-site                   latest              fcaa5e0ee8f2        9 hours ago         109 MB
10.70.0.28:5000/static-site   <none>              60ceae523ef0        14 hours ago        109 MB
registry                      2                   9d0c4eabab4d        3 weeks ago         33.2 MB

Without the right SSL setup I wouldn’t be able to push images.

$ docker -D push 10.70.0.28:5000/static-site
The push refers to a repository [10.70.0.28:5000/static-site]
6ce8e637d806: Layer already exists
a552ca691e49: Layer already exists
7487bf0353a7: Layer already exists
8781ec54ba04: Layer already exists
latest: digest: sha256:eb52222d9a7e00426ad94eacaf442dd07e52243ecec7f328537515f0b4c035da size: 1155

Now I have an internal, private repository that is using SSL so that I don’t have to reconfigure all the Docker nodes to use an insecure repository, though one would still have to ensure the cacert is installed on all the Docker nodes.

Conclusion

The hardest part of this is SSL, which I’m sure I’ve done wrong but is working. Please let me know of any ways to do this better. :)