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coffer/example/README.md
Armin Friedl f4b9c8000f
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2020-08-02 23:34:19 +02:00

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Here you can find a simple example on how to run coffer.

Run the example

To run the example, simply execute:

docker-compose up

This should print out:

 @@@@@@@   @@@@@@   @@@@@@@@  @@@@@@@@  @@@@@@@@  @@@@@@@
@@@@@@@@  @@@@@@@@  @@@@@@@@  @@@@@@@@  @@@@@@@@  @@@@@@@@
!@@       @@!  @@@  @@!       @@!       @@!       @@!  @@@
!@!       !@!  @!@  !@!       !@!       !@!       !@!  @!@
!@!       @!@  !@!  @!!!:!    @!!!:!    @!!!:!    @!@!!@!
!!!       !@!  !!!  !!!!!:    !!!!!:    !!!!!:    !!@!@!
:!!       !!:  !!!  !!:       !!:       !!:       !!: :!!
:!:       :!:  !:!  :!:       :!:       :!:       :!:  !:!
 ::: :::  ::::: ::   ::        ::        :: ::::  ::   :::
 :: :: :   : :  :    :         :        : :: ::    :   : :

PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
TERM=xterm
container=podman
HOSTNAME=f7a1614d8752
HOME=/root
CLIENT_SECRET=SECRETKEY
client
0

Where CLIENT_SECRET is the secret set into the environment of printenv in the client. printenv is the coffer'ed process.

Note that if you connect to a shell in the client container you are not able to retrieve the secret. The secret only exists in the environment of the coffer'ed process. It does not even exist in some parent process of the coffer'ed process, as coffer reaps itself while starting the sub-process. This is quite different from other alternatives that either set the secrets into the environment of the container, or into a volume on the container. Both of which are accessible (with more or less effort) from anyone that has access to the container.

Also note how the whole server container, despite being able to service hundreds of clients in parallel, uses less than 3 MB in total.

Setup and Configuration

In this example we create a coffer server with some client secrets and a simple client container. The container are built, run and connected a shared network via docker-compose.

Both, the client and the server, need a certificate. The client for authenticating with the server, and the server for decrypting the client secrets.

Certificates can be generated with:

coffer-companion certificate certificate.cert

Furthermore, the secrets need to be authorized. Even though a coffer server can handle secrets for multiple clients, a client can only request its own secrets. Secrets retrieval is authorized by the public key of the client. You can get the public key by

coffer-companion info certificate.cert

The public key must be put into the id section of a secret. For example, our secrets contain a section like this:

[client]
id = "452B0788D966059B21DB04FF37BC6161072B15EA2CDF88A5040FEEAB89D1143A"
CLIENT_SECRET = "SECRETKEY"

Finally, the promise of coffer is that certificates are the fundamental trust anchor. This also means they are the only thing you have to care about for security of your secrets. Consequently, secrets themselves are encrypted with the server certificate:

coffer-companion encrypt --certificate certificate.cert --out config.enc --yaml config.toml

Encoffering the client

You may have noticed that the actual client program (printenv) is not run directly. Instead the Dockerfile contains an entrypoint like this:

ENTRYPOINT ["coffer-client"]

CMD ["--certificate", "client.cert", \
     "--server-address", "server:9187", \
     "--", \
     "printenv"]

The coffer client will connect to the server and retrieve its secrets. Afterwards it sets the secrets into the process environment and replaces its own process image with the coffer'ed command.

The major drawback of this approach is that you have to build your own images. If you want to coffer your own software this is probably only a minor inconvenience. For pre-build images like e.g. the official postgres image this means you have to derive your own image for and coffer the entrypoint. For postgres this might look like:

FROM postgres:12-alpine

COPY ./coffer-client /usr/local/bin
COPY ./postgres.cert .

ENTRYPOINT ["coffer-client", \
            "--certificate", "postgres.cert", 
            "--server-address", "server:9187", 
            "--", 
            "docker-entrypoint.sh"]

CMD ["postgres"]