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Client

The Cert Warden Client is a Docker container that manages the certificates on a Docker host. On start it fetches the current key and cert from Cert Warden, after which it runs an https server that listens for update payloads from Cert Warden. When an update is received, it updates the key and cert on disk and optionally restarts other Docker containers (which may be desired if those containers don't automatically start using new certificates when they're changed on the disk).

The Cert Warden Client is only intended to be used in a Docker container.

Configuration​

The first step to using Cert Warden client is to enable it on the relevant certificate in Cert Warden. Go to the certificate, expand the Post Processing section and click Enable under Cert Warden Client.

This will generate a Client AES Key that you will need to copy and paste into the client configuration.

Client Example Docker Run:

/usr/bin/docker run --name certwardenclient \
  -p 5055:5055 \
  -v /var/run/docker.sock:/var/run/docker.sock \
  -v /persist/certwardenclient/certs:/opt/certwarden/certs \
  -e TZ=America/New_York \
  -e CW_CLIENT_FILE_UPDATE_TIME_START='04:30' \
  -e CW_CLIENT_FILE_UPDATE_TIME_END='05:45' \
  -e CW_CLIENT_FILE_UPDATE_DAYS_OF_WEEK='Mon Wed Thu' \
  -e CW_CLIENT_RESTART_DOCKER_CONTAINER0='cert_using_app' \
  -e CW_CLIENT_AES_KEY_BASE64='[the key Cert Warden CertHub generated]' \
  -e CW_CLIENT_SERVER_ADDRESS='https://certwarden.example.com' \
  -e CW_CLIENT_KEY_NAME='app.example.com' \
  -e CW_CLIENT_KEY_APIKEY='abcd1234' \
  -e CW_CLIENT_CERT_NAME='app.example.com' \
  -e CW_CLIENT_CERT_APIKEY='1234abcd' \
  ghcr.io/gregtwallace/certwarden-client:latest

One data mount is needed and this is for the storage of key and certificate files. You should mount this same location to containers using the certificates but those containers should mount using the read-only option.

tip

The docker.sock mount is only required when you want the client to auto restart other containers.

warning

Mounting docker.sock adds another attack vector. If a container mounting docker.sock is compromised, the host is effectively compromised. Ensure you understand these risks.

Only these environment variables are mandatory:

  • CW_CLIENT_AES_KEY_BASE64 - The base64 raw url encoding of AES key used for communication between server and client. Cert Warden generates this on the Server side. It is located under "Edit Certificate" > "Post Processing".
  • CW_CLIENT_SERVER_ADDRESS - DNS name of the Cert Warden server. Must start with https and have a valid ssl certificate.
  • CW_CLIENT_KEY_NAME - Name of the private key in Cert Warden server.
  • CW_CLIENT_KEY_APIKEY - API Key of private key in Cert Warden server.
  • CW_CLIENT_CERT_NAME - Name of certificate in Cert Warden server.
  • CW_CLIENT_CERT_APIKEY - API Key of certificate in Cert Warden server.

Additional environment variables can be viewed at: https://github.com/gregtwallace/certwarden-client/blob/main/pkg/main/config.go

Of particular note are the options for restarting containers and for setting a time window to permit certificate updates (and container restarts). These options are helpful to avoid restarts at inopportune times.