gencert/README.md

# gencert

This script generates x509 server certificate (with all IPs in SAN) signed by a
self-signed CA.

## Purpose

The whole idea is to run the ``gencert.sh`` script right before starting the
service and then, making sure the reverse proxy updates its main CA bundle
right before starting.

Some services require the certificate on their backend and would not be
satisfied with the TLS termination elsewhere.

For example, one of such services is Minio. It [requires](https://github.com/minio/minio/issues/6093) its certificate in order
to enable SSE-C (Server Side Encryption with Customer provided keys).

## How does this script work

This script will always produce a self-signed x509 certificate with the IP
addresses embedded to x509's SAN.

It will also produce a CA certificate and can be used by other services
which may need to authenticate against this self-signed certificate.

The authentication works in a way that a public CA certificate will be
used by the client in order to validate the server's certificate.

- generate CA certificate if does not find any
- always generate server certificate on startup to ensure all IP addresses
  are in x509 SAN
- warn if the CA certificate is about to expire (<30 days till expiration)
- regenerate the CA certificate if it finds it has expired

> The CA certificate will be valid for 3650 days (10 years)
> The server certifcate will be valid for 365 days (1 year)
> The x509 certs are ECDSA with prime256v1 curve and SHA256 signatures

## Examples

### Minio and Docker Registry services with Traefik reverse proxy

- docker-compose.yml

> I intentionally left only the gencert-related lines.
>
> If you are using Alpine based image, the correct CA certificates path is
> ``/usr/local/share/ca-certificates/``, otherwise one of these
> https://golang.org/src/crypto/x509/root_linux.go

```
services:
  minio:
    image: minio/minio
    volumes:
      - /srv/data/minio/certs:/root/.minio/certs
      - /srv/services/gencert/gencert.sh:/gencert.sh:ro
    entrypoint: sh -c "cd /root/.minio/certs && /gencert.sh --cn minio.example.com && minio server /data"
    environment:
      - "MINIO_ACCESS_KEY=redacted"
      - "MINIO_SECRET_KEY=redacted"

  registry:
    image: registry:2.6.2
    volumes:
      - /srv/services/gencert/gencert.sh:/gencert.sh:ro
      - /srv/data/registry/certs:/certs
    entrypoint: sh -c "cd /certs && /gencert.sh --cn registry.example.com && registry serve /etc/docker/registry/config.yml"
    environment:
      REGISTRY_HTTP_TLS_CERTIFICATE: '/certs/public.crt'
      REGISTRY_HTTP_TLS_KEY: '/certs/private.key'

  traefik:
    image: traefik:1.6-alpine
    volumes:
      - /srv/data/minio/certs/ca.crt:/usr/local/share/ca-certificates/minio_ca.crt:ro
      - /srv/data/registry/certs/ca.crt:/usr/local/share/ca-certificates/registry_ca.crt:ro
    command: sh -c "update-ca-certificates && traefik"
    depends_on:
      - minio
      - registry
```

## Testing

I have added a simplistic script [testme.sh](testme.sh) that helps to test this
script in the following  Linux distributions:

- Alpine 3.4
- Alpine 3.7
- Ubuntu Bionic
- Debian Stretch
- CentOS 7

> Alpine 3.4 - as it has old getent which [misses](https://git.alpinelinux.org/cgit/aports/commit/?id=2e4493888fff74afc6a6ef6257aeea469df32af5) ahostsv4