Allow config override in docker image

Dockerfile

@@ -6,4 +6,9 @@ RUN yarn install \
  && yarn build
 
 FROM docker.io/nginx:alpine
+
+# Copy the dynamic config script
+COPY ./docker/dynamic-config.sh /docker-entrypoint.d/99-dynamic-config.sh
+
+# Copy the built app from the first build stage
 COPY --from=builder /app/target /usr/share/nginx/html

doc/docker.md

@@ -56,3 +56,27 @@ docker run \
     --publish 80:80 \
     hydrogen
 ```
+
+You can override the default `config.json` using the `CONFIG_OVERRIDE` environment variable. For example to specify a different Homeserver and :
+
+```
+docker run \
+    --name hydrogen \
+    --publish 80:80 \
+    --env CONFIG_OVERRIDE='{
+  "push": {
+    "appId": "io.element.hydrogen.web",
+    "gatewayUrl": "https://matrix.org",
+    "applicationServerKey": "BC-gpSdVHEXhvHSHS0AzzWrQoukv2BE7KzpoPO_FfPacqOo3l1pdqz7rSgmB04pZCWaHPz7XRe6fjLaC-WPDopM"
+  },
+  "defaultHomeServer": "https://fosdem.org",
+  "themeManifests": [
+    "assets/theme-element.json"
+  ],
+  "defaultTheme": {
+    "light": "element-light",
+    "dark": "element-dark"
+  }
+}' \
+    hydrogen
+```

docker/dynamic-config.sh

@@ -0,0 +1,8 @@
+#!/bin/sh
+
+set -eux
+
+# Use config override environment variable if set
+if [ -n "${CONFIG_OVERRIDE:-}" ]; then
+    echo "$CONFIG_OVERRIDE" > /usr/share/nginx/html/config.json
+fi