Ok, I managed to find a solution
ports:
- ${PORT}:443
volumes:
- jsreport:/jsreport
- certs:/certs
environment:
httpsPort: 443
certificate_key: /certs/${SSL_KEY}
certificate_cert: /certs/${SSL_CERT}
I needed to specify the certs directory from the root...
And the config path needed a ' _ ' not a ' . ' , I don't know how I made that assumption