diff --git a/Dockerfile b/Dockerfile
index 3eb5782..27ab84b 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -67,8 +67,9 @@ RUN adduser -D -H -s /sbin/nologin pixad && \
     mkdir -p /var/lib/pixa /etc/pixa && \
     chown pixad:pixad /var/lib/pixa
 
-# Copy default config (edit signing_key before use)
-COPY config.example.yml /etc/pixa/config.yml
+# Copy the image config; signing_key comes from PIXA_SIGNING_KEY.
+# Mount a file over /etc/pixa/config.yml to override anything else.
+COPY config.docker.yml /etc/pixa/config.yml
 
 USER pixad
 WORKDIR /var/lib/pixa
diff --git a/config.docker.yml b/config.docker.yml
new file mode 100644
index 0000000..548b45a
--- /dev/null
+++ b/config.docker.yml
@@ -0,0 +1,11 @@
+# Pixa configuration baked into the Docker image.
+#
+# The signing key is read from the PIXA_SIGNING_KEY environment
+# variable; startup aborts naming it when it is unset. Every other key
+# is omitted so its default applies. Operators who need more (an
+# allowlist, metrics, and so on) mount their own file over
+# /etc/pixa/config.yml.
+
+signing_key: "${ENV:PIXA_SIGNING_KEY}"
+state_dir: /var/lib/pixa
+port: 8080