Kill off deprecated "config-on-the-fly" docker mode (#6918)

Lots of people seem to get confused by this mode, and it's been deprecated
since Synapse 1.1.0. It's time for it to go.

1 files changed, 14 insertions, 9 deletions

diff --git a/docker/README.md b/docker/README.md
index 9f112a01d0..8c337149ca 100644
--- a/docker/README.md
+++ b/docker/README.md
@@ -110,12 +110,12 @@ argument to `docker run`.
 
 ## Legacy dynamic configuration file support
 
-For backwards-compatibility only, the docker image supports creating a dynamic
-configuration file based on environment variables. This is now deprecated, but
-is enabled when the `SYNAPSE_SERVER_NAME` variable is set (and `generate` is
-not given).
+The docker image used to support creating a dynamic configuration file based
+on environment variables. This is no longer supported, and an error will be
+raised if you try to run synapse without a config file.
 
-To migrate from a dynamic configuration file to a static one, run the docker
+It is, however, possible to generate a static configuration file based on
+the environment variables that were previously used. To do this, run the docker
 container once with the environment variables set, and `migrate_config`
 command line option. For example:
 
@@ -127,15 +127,20 @@ docker run -it --rm \
     matrixdotorg/synapse:latest migrate_config
 ```
 
-This will generate the same configuration file as the legacy mode used, but
-will store it in `/data/homeserver.yaml` instead of a temporary location. You
-can then use it as shown above at [Running synapse](#running-synapse).
+This will generate the same configuration file as the legacy mode used, and
+will store it in `/data/homeserver.yaml`. You can then use it as shown above at
+[Running synapse](#running-synapse).
+
+Note that the defaults used in this configuration file may be different to
+those when generating a new config file with `generate`: for example, TLS is
+enabled by default in this mode. You are encouraged to inspect the generated
+configuration file and edit it to ensure it meets your needs.
 
 ## Building the image
 
 If you need to build the image from a Synapse checkout, use the following `docker
  build` command from the repo's root:
- 
+
 ```
 docker build -t matrixdotorg/synapse -f docker/Dockerfile .
 ```