Publish the secrets proxy as an image

.github/workflows/on-main-merge.yml

@@ -115,3 +115,25 @@ jobs:
           labels: ${{ steps.meta.outputs.labels }}
           cache-from: type=gha
           cache-to: type=gha,mode=max
+
+      - name: Extract proxy image metadata
+        id: proxy-meta
+        uses: docker/metadata-action@v6
+        with:
+          images: ghcr.io/${{ github.repository }}/proxy
+          tags: |
+            type=ref,event=branch
+            type=sha
+            type=raw,value=latest,enable={{is_default_branch}}
+
+      - name: Build and push proxy image
+        uses: docker/build-push-action@v7
+        with:
+          context: ./deploy/proxy
+          file: ./deploy/proxy/Dockerfile
+          platforms: linux/amd64,linux/arm64
+          push: true
+          tags: ${{ steps.proxy-meta.outputs.tags }}
+          labels: ${{ steps.proxy-meta.outputs.labels }}
+          cache-from: type=gha,scope=proxy
+          cache-to: type=gha,mode=max,scope=proxy

.github/workflows/on-pull-request.yml

@@ -133,6 +133,9 @@ jobs:
       - name: Build container image
         run: docker build -t drukbox:validate .
 
+      - name: Build proxy image
+        run: docker build -t drukbox-proxy:validate deploy/proxy
+
   api-tests:
     name: Run API Tests (docker provider)
     runs-on: ubuntu-latest

AGENTS.md

@@ -58,7 +58,7 @@ src/
   templates/         # Template API, models, service, and janitor
   conftest.py        # Test env defaults and database reset fixture
 alembic/             # Database migrations
-deploy/proxy/        # The secrets proxy: a mitmproxy addon, mounted into the official image
+deploy/proxy/        # The secrets proxy: a mitmproxy addon and the Dockerfile of its image
 api-tests/           # Playwright black-box API tests
 docs/                # Architecture, networking, deploy, add-a-provider
 Dockerfile           # Single image: API + cron commands + migrations

deploy/proxy/Dockerfile

@@ -0,0 +1,5 @@
+FROM mitmproxy/mitmproxy:12.2.3
+
+COPY swap.py /addon/swap.py
+
+CMD ["mitmdump", "--listen-host=0.0.0.0", "--listen-port=8880", "--set=flow_detail=1", "-s", "/addon/swap.py"]

deploy/proxy/swap.py

@@ -12,6 +12,7 @@
 import ipaddress
 import json
 import logging
+import os
 import socket
 import time
 import urllib.parse
@@ -105,7 +106,12 @@ def __init__(self) -> None:
         self._upstreams_known = False
 
     def load(self, loader) -> None:
-        loader.add_option("exchange_url", str, "", "Address of the secrets exchange process.")
+        loader.add_option(
+            "exchange_url",
+            str,
+            os.environ.get("SECRETS_EXCHANGE_URL", ""),
+            "Address of the secrets exchange process.",
+        )
 
     def configure(self, updated: set[str]) -> None:
         if "exchange_url" in updated:

docs/architecture.md

@@ -32,7 +32,7 @@ hosts.service      host lifecycle behavior (HostService)
 host_secrets.api   host secret registration concerns only
 host_secrets       built-in catalog, placeholders, delivery at provisioning
 secrets_exchange   the secrets exchange process behind the secrets proxy
-deploy/proxy       the secrets proxy addon, run by the official mitmproxy image
+deploy/proxy       the secrets proxy addon and the Dockerfile of its image
 templates.api      template request/response concerns only
 templates.service  template build and delete behavior (TemplateService)
 providers/<name>   one package per VM provider
@@ -139,7 +139,7 @@ and the proxy's CA in `SECRETS_PROXY_CA`, which it installs at boot. A box
 with a `github` secret also points git at gh for its credential and rewrites
 SSH remotes to HTTPS, so git sends the placeholder as a Basic password and
 the proxy swaps it.
-The proxy is the official mitmproxy image with the addon in `deploy/proxy`.
+The proxy is the official mitmproxy image with the addon in `deploy/proxy` built in.
 It terminates TLS only for the hosts the exchange lists at `/upstreams`, the
 hosts with a registered secret, and tunnels every other host blind. For a
 request with a placeholder it asks the exchange at `/authorize`, with the

docs/deploy.md

@@ -8,7 +8,9 @@ behind these defaults, read [Security](security.md).
 
 One image serves everything — API, maintenance commands, migrations.
 It's published to `ghcr.io/czpython/drukbox` on every release; build
-`docker build -t ghcr.io/czpython/drukbox .` only to run a local change.
+`docker build -t ghcr.io/czpython/drukbox .` only to run a local change. The
+secrets proxy image, `ghcr.io/czpython/drukbox/proxy`, is published beside it
+with the same tags.
 
 ```bash
 IMAGE=ghcr.io/czpython/drukbox:latest
@@ -274,8 +276,11 @@ A sandbox never holds a real third-party credential. It holds a placeholder,
 and it sends its HTTPS through the secrets proxy. The proxy swaps the
 placeholder for the real credential on the way out. Two pieces run this:
 
-- **The proxy** is the official `mitmproxy/mitmproxy` image with the addon
-  `deploy/proxy/swap.py` mounted in. It terminates TLS only for the hosts
+- **The proxy** is `ghcr.io/czpython/drukbox/proxy`: the official
+  `mitmproxy/mitmproxy` image with the addon `deploy/proxy/swap.py` built in.
+  It listens on 8880 and reads the exchange address from
+  `SECRETS_EXCHANGE_URL`. A checkout can mount the addon into the official
+  image instead. It terminates TLS only for the hosts
   that have a registered secret and tunnels every other host blind. It
   refuses a destination that resolves to a loopback, private, link-local, or
   metadata address. It makes its CA on first start and keeps it in a volume.
@@ -294,18 +299,12 @@ services:
       SECRETS_EXCHANGE_BIND_HOST: 0.0.0.0
 
   proxy:
-    image: mitmproxy/mitmproxy:12.2.3
-    command:
-      - mitmdump
-      - --listen-host=0.0.0.0
-      - --listen-port=8880
-      - --set=exchange_url=http://exchange:8781
-      - --set=flow_detail=1
-      - -s=/addon/swap.py
+    image: ghcr.io/czpython/drukbox/proxy:latest
+    environment:
+      SECRETS_EXCHANGE_URL: http://exchange:8781
     ports:
       - "8880:8880"
     volumes:
-      - ./deploy/proxy/swap.py:/addon/swap.py:ro
       - secrets-proxy-ca:/home/mitmproxy/.mitmproxy
 
 volumes: