Add config option redis.password_path (#17717)

Adds the option to load the Redis password from a file, instead of
giving it in the config directly. The code is similar to how it’s done
for `registration_shared_secret_path`. I changed the example in the
documentation to represent the best practice regarding the handling of
secrets.

Reading secrets from files has the security advantage of separating the
secrets from the config. It also simplifies secrets management in
Kubernetes.

1 files changed, 7 insertions, 1 deletions

diff --git a/docs/usage/configuration/config_documentation.md b/docs/usage/configuration/config_documentation.md

index 08eedc03b7..29f3528c7e 100644
--- a/docs/usage/configuration/config_documentation.md
+++ b/docs/usage/configuration/config_documentation.md
@@ -4524,6 +4524,9 @@ This setting has the following sub-options:
 * `path`: The full path to a local Unix socket file. **If this is used, `host` and
  `port` are ignored.** Defaults to `/tmp/redis.sock'
 * `password`: Optional password if configured on the Redis instance.
+* `password_path`: Alternative to `password`, reading the password from an
+   external file. The file should be a plain text file, containing only the
+   password. Synapse reads the password from the given file once at startup.
 * `dbid`: Optional redis dbid if needs to connect to specific redis logical db.
 * `use_tls`: Whether to use tls connection. Defaults to false.
 * `certificate_file`: Optional path to the certificate file
@@ -4537,13 +4540,16 @@ This setting has the following sub-options:
 
   _Changed in Synapse 1.85.0: Added path option to use a local Unix socket_
 
+  _Changed in Synapse 1.116.0: Added password\_path_
+
 Example configuration:
 ```yaml
 redis:
   enabled: true
   host: localhost
   port: 6379
-  password: <secret_password>
+  password_path: <path_to_the_password_file>
+  # OR password: <secret_password>
   dbid: <dbid>
   #use_tls: True
   #certificate_file: <path_to_the_certificate_file>