Use cfssl in a multi-stage build docker image

CFSSL is Cloudflare's PKI and TLS toolkit. I recently wanted to use to generate a self signed certificate in a docker file.

You can technically install cfssl in a multitude of ways in whatever docker image you are using. There is a simpler approach though using Docker's multi-stage builds.

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Let us say you have a registry image, code below:

FROM registry

LABEL maintainer="[e-mail]"

And to use cfssl, you can do something like:

FROM cfssl/cfssl AS cfssl

WORKDIR /

# Generate certificate
COPY ca-csr.json /
RUN cfssl gencert -initca ca-csr.json | cfssljson -bare ca -
RUN rm /ca-key.pem

FROM registry

LABEL maintainer="[e-mail]"

# Copy it to the registry
COPY --from=cfssl /ca.csr /certs/selfsigned.crt
COPY --from=cfssl /ca.pem /certs/selfsigned.key

ca-csr.json

{
  "CN": "ML Sutdio CA",
  "hosts": [
    "mlstudio-registry.default.svc.cluster.local"
  ],
  "key": {
    "algo": "rsa",
    "size": 2048
  },
  "names": [{
    "C": "NZ",
    "O": "ML Studio"
  }]
}

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