haproxy/README.md

# Intro

> Русская версия: [README.ru-RU.md](README.ru-RU.md)

[HAProxy](https://www.haproxy.org/) is a TCP/HTTP load balancer and reverse proxy. Here it is the public edge of a BitDeals site: it terminates TLS on 443, forwards everything to the web container, and routes ACME challenges to certbot.

HAProxy running in a docker container with a baked-in configuration.

This repository covers the docker deployment only. The image is `bitnami/haproxy` with one file copied into it.

# Usage

The container has two ports, **80** and **443**, and both are the public site.

The third channel is not a port: the HAProxy runtime API listens on a unix
socket at `/var/lib/haproxy/admin.sock`, on a volume shared with the
[certbot](https://git.bitdeals.org/private/certbot) container, which uses it to
install a renewed certificate into the running process without a restart. The
API is `level admin` and has no authentication, so who can open it is decided by
file permissions — see Notes.

There is one environment variable, `XFF_HMAC_KEY`, and it is optional.
Everything else is in `docker/haproxy.cfg`, which is copied into the image at
build time, so changing the routing means rebuilding and redeploying.

The certificate is read from `/usr/local/etc/haproxy/certificates/site.pem`,
mounted **read-only** from a volume shared with certbot. It must exist before
the container starts — see Notes.

## docker-compose

```yaml
services:
  haproxy:
    build:
      context: https://git.bitdeals.org/private/haproxy.git
      dockerfile: ./docker/Dockerfile
    image: registry.bitdeals.org/haproxy
    restart: unless-stopped
    depends_on:
      - nginx
      - certbot
    volumes:
      - certificates:/usr/local/etc/haproxy/certificates:ro
      - haproxy_admin:/var/lib/haproxy   # runtime API socket — certbot only
    ports:
      - "80:80"
      - "443:443"

volumes:
  certificates:
  haproxy_admin:
```

The two backends are named after the services they reach: `nginx:80` for the
site and `certbot:380` for ACME challenges. Both names have to resolve inside
the compose project, so those services must share a network with this one.

## docker cli

```sh
docker run -d \
  -p 80:80 \
  -p 443:443 \
  -v certificates:/usr/local/etc/haproxy/certificates:ro \
  registry.bitdeals.org/haproxy
```

Anything after the image name replaces the daemon's own arguments, so a config
check against a mounted file needs no new image:

```sh
docker run --rm -v "$PWD/docker/haproxy.cfg:/tmp/haproxy.cfg:ro" \
  registry.bitdeals.org/haproxy -c -f /tmp/haproxy.cfg
```

## build and publish

A push to `main` builds and publishes the image
(`.gitea/workflows/build.yaml`), tagging it three ways: `<version>.<sha7>` to
deploy by, `<version>` to read, and `latest` for compose and Watchtower. A
nightly cron rebuilds from the same sources. By hand, when the registry
credentials are at hand:

```sh
docker build . --file docker/Dockerfile --tag registry.bitdeals.org/haproxy
docker push registry.bitdeals.org/haproxy
```

**The build context is the repository root**, not `docker/`: the Dockerfile
copies `./docker/haproxy.cfg`, so a context of `./docker` cannot see it and the
build fails on the `COPY`.

# Parameters

Container images are configured using parameters passed at runtime.

|Parameter|Function|
|:--------|:-------|
|-p 80|Plain HTTP. Redirects to HTTPS with a 301, except the ACME challenge path, which must stay reachable here for renewals to work|
|-p 443|HTTPS. Needs `site.pem` in the certificates volume before the container starts|
|-v /usr/local/etc/haproxy/certificates|Certificate directory, read-only. Only `site.pem` is read, at bind time. certbot writes it through the same volume mounted read-write at `/etc/certificates`|
|-v /var/lib/haproxy|Runtime API socket (`admin.sock`, `level admin`, **no authentication**). Mount it into certbot and nothing else — see Notes|
|-e XFF_HMAC_KEY|Optional, base64. Set, the visitor's address is replaced by an HMAC of it in `X-Client-Id` and never passed on; empty, no such header is sent. Generate with `openssl rand -base64 32` — see Notes|

Routing, timeouts and TLS settings are not parameters: they live in
`docker/haproxy.cfg` and ship inside the image.

# Notes

- **`site.pem` must exist before the container starts.** `bind ... ssl crt` is
  resolved while the configuration is parsed, so an empty volume is a fatal
  start-up error, not a warning — HAProxy exits, and without a restart policy it
  stays down. certbot writes a self-signed placeholder on its own first start
  precisely to break this circle, which is why the service ships with
  `restart: unless-stopped`; order it after certbot with `depends_on` in a
  project that defines one.
- **A certificate installed over the runtime API lives in memory only.** That is
  why the volume is mounted read-only here: `set ssl cert` + `commit ssl cert`
  never write to disk. The file on the volume is certbot's copy, and it is what
  HAProxy re-reads after a restart — so the two paths agree without HAProxy
  needing write access.
- **The runtime API is a full administrative channel with no password.** Anyone
  who can open it can install a different certificate and private key, redirect
  a backend to another address, or take servers out of rotation — that is,
  silently man-in-the-middle the site. Treat access to `admin.sock` as
  equivalent to holding the TLS private key, and mount that volume into certbot
  and nothing else. `expose-fd listeners`, which would additionally hand a
  client of the socket the listening sockets themselves, is deliberately **not**
  set: it exists for seamless reloads, which this image never performs.
- **A unix socket, because a port cannot be restricted.** `expose:` publishes
  nothing to the host but restricts nothing either, and docker networks have no
  per-port rules — so a TCP runtime API is open to every container sharing a
  network, which here includes nginx, since HAProxy must be able to call *it*.
  A socket on a volume is reachable only by containers that mount the volume,
  and that is the whole access-control story. It also keeps the private key,
  which crosses this channel on every renewal, off the network.
- **HAProxy needs write access to the socket's directory, not just the file.**
  It binds by creating `<path>.<pid>.tmp` and renaming it over the target — so
  the image creates `/var/lib/haproxy` owned by uid 1001, and docker carries
  that ownership onto an empty named volume mounted there. The rename is also
  why a stale socket left by a previous run is harmless. certbot connects as
  root and is unaffected by the `mode 660`.
- **The redirect to HTTPS carries one exception, and it is load-bearing.**
  Port 80 answers 301 for everything except `/.well-known/acme-challenge/`,
  which Let's Encrypt validates over plain HTTP — redirect that and every
  renewal stops. The rule is written above `use_backend` because that is the
  order it runs in: `http-request` rules are evaluated before backend selection
  whatever the file says, and HAProxy warns when the two disagree.
- **HSTS is one day, not the customary year.** It is a one-way door: a browser
  that has seen the header refuses plain HTTP to this host until it expires, and
  nothing server-side can call that back. A day keeps a lapsed certificate
  recoverable. Raise it in steps — 86400, 2592000, 31536000 — once renewals have
  been seen to work. `includeSubDomains` and `preload` are deliberately absent:
  the first binds names this proxy does not serve, the second is effectively
  permanent.
- **Backend addresses are re-resolved, and that is not the default.** Both
  `server` lines carry `resolvers docker`, so the `nginx` and `certbot` names
  are looked up again while HAProxy runs. Without it a name is resolved once at
  boot and kept for the life of the process, and a container recreated on a new
  IP — which is what Watchtower does on every deploy — is never noticed.
  `init-addr libc,none` is the other half: it lets HAProxy start when a backend
  is not up yet, instead of refusing to parse a name it cannot resolve.
- **Logging goes to stdout, and `option dontlog-normal` makes it errors-only.**
  `log stdout format raw local0` needs no syslog daemon — `docker logs` collects
  it. A successful request writes nothing; a 503, a backend with no server, a
  refused handshake do. Drop `dontlog-normal` deliberately if a full access log
  is wanted, and understand that it is also what keeps the volume down.
- **There are two loggers, and forgetting the second one leaks addresses.**
  `option httplog` is never used: its default format opens with `%ci:%cp`, which
  would put every visitor's address into `docker logs` and undo the pseudonym the
  frontends mint. A hand-written `log-format` puts the pseudonym in that first
  field instead. The trap is `error-log-format`, which covers what happens
  *before* a transaction exists — a refused TLS handshake, and TLS 1.2 is now
  the floor — and whose default opens the same way. Both are set here. The
  pseudonym is therefore computed by a `tcp-request connection` rule on accept,
  in `sess` scope, because an http-phase rule would not have run yet when a
  handshake fails.
- **Only the method and path are logged, never the query string.** `%{+Q}r`
  would carry it, and a token that ever appeared in a URL would be written down
  for as long as the log is kept.
- **The visitor's address stops here.** There is no `option forwardfor`:
  `X-Forwarded-For` is deleted in both frontends and never filled in, so nothing
  behind this proxy can log an address it was never given. `X-Client-Id` carries
  a pseudonym instead — HMAC-SHA256 of the address under `XFF_HMAC_KEY`. Being
  one-to-one with the address it is exactly as good a rate-limiting key, and
  without the key it is not reversible. HMAC rather than a bare digest because
  IPv4 is 2^32 values and an unkeyed hash of an address is brute-forced in
  seconds.
- **`XFF_HMAC_KEY` is optional, and an empty one disables the feature rather
  than weakening it.** Unset, no `X-Client-Id` is sent at all and a rate limit
  downstream falls back to one bucket shared by every visitor; set, each visitor
  gets their own. What never happens is a pseudonym derived from an empty key.
  A value that is not valid base64 stops the container at configuration
  parsing — it cannot degrade quietly. Rotating the key resets rate-limit
  buckets (invisible to users) and changes every pseudonym, so activity either
  side of a rotation cannot be linked.
- **Both deletes are unconditional.** `X-Forwarded-For` and `X-Client-Id` are
  dropped whether or not a key is configured, so a header a client sent can
  never be mistaken downstream for one this proxy minted. Same for
  `X-Forwarded-Proto`, which each frontend sets to its own scheme rather than
  passing on the client's claim.
- **The consumer must still be told to use it.** A downstream rate limit keyed
  on the socket address — nginx's `$binary_remote_addr`, ДС's
  `request.client.host` — sees this proxy for every request and degenerates to
  one shared bucket. It has to key on `X-Client-Id`, and trust that header only
  from this proxy's address; `frontend/docker/rate-limit.conf` in the bitdeals-ng
  repository is the worked example.
- **TLS is pinned in `global`, not left to OpenSSL.** TLS 1.2 is the floor,
  the cipher list is ECDHE-only in both ECDSA and RSA variants — certbot issues
  ECDSA, the self-signed placeholder is RSA — and session tickets are off so
  forward secrecy is not undone by a long-lived ticket key. `alpn h2,http/1.1`
  on the bind offers HTTP/2 to browsers; the backend stays HTTP/1.1 and HAProxy
  translates. **No HSTS header is sent**, deliberately: it would be premature
  while port 80 still serves the site rather than redirecting, and it is hard to
  take back once browsers have cached the policy.
- **`timeout http-request 10s` is what bounds the header phase**, and
  `timeout client` cannot stand in for it: that one is an *inactivity* timeout
  and resets on every byte received, so a client dripping a byte at a time holds
  a connection open indefinitely. This one is absolute.
- **The process runs as uid 1001 and still binds 80 and 443.** That works
  because Docker sets `net.ipv4.ip_unprivileged_port_start=0` in containers by
  default; a host or runtime that restores the traditional value will make the
  container fail to bind.
- **The base image is unpinned.** `FROM bitnami/haproxy` means `:latest`, and
  the nightly rebuild cron picks up whatever that tag points at — a HAProxy
  minor version can change under a build nobody triggered, and Watchtower then
  rolls it out. Pin `FROM bitnami/haproxy:<version>` for reproducible builds.