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Add README, SPEC and tool evaluation, closes #1

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Initial documents: what smallwebwaf is and why, the proposed feature list, the design spec with the rule file format and the open design questions, and the survey of existing tools.

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# smallwebwaf SPEC (draft): protective reverse-proxy sidecar
Status: second draft, with the owner's rulings on storage, logging and metrics
applied. Nothing has been built yet. `EVALUATION.md` beside this file explains why no existing tool was
chosen. Points that turn on an owner decision are collected under "Questions for
the owner" and are marked "(open)" where they appear.
## Purpose
One small container that sits between traefik and one application container. The
traefik router for the public hostname points at the sidecar; the sidecar
forwards to the application. The sidecar limits request and byte rates per
client, detects attacks, blocks abusers for a time and bans repeat offenders,
consults IP reputation sources, looks up the AS number and country of each
client, scales its limits for listed AS numbers and countries, and sends alerts.
Everything is configured by environment variables, apart from the attack
detection rules, which are read from a directory of hand-editable text files.
## Non-goals
- TLS termination, certificates, hostname routing: traefik's job.
- More than one upstream application per sidecar. Run one sidecar per app.
- Browser challenges (captcha, proof of work). If wanted, chain Anubis between
the sidecar and the app.
- Defence against traffic floods that saturate the host's network link. That
needs help upstream of the host.
- A web UI or a configuration file. Settings are environment variables; the
only files read are the rule files, which hold one regex per line and nothing
more elaborate.
- Sharing ban state between sidecars in the first version (open, see
Questions).
## Architecture
- One statically linked Go binary in one container, running as a non-root user,
read-only root filesystem, one writable volume for state.
- Three listeners, of which only the first is routed by traefik:
- the proxy listener;
- a metrics listener serving Prometheus metrics, which can be switched off;
- an admin listener for health and ban management.
- Components inside the process:
- Client identification: works out the real client IP from
`X-Forwarded-For`, trusting only configured proxy netblocks.
- Lookup: AS number and country from local database files, held in memory.
- Reputation: static blocklists fetched on a schedule; DNSBL and reputation
API queries made in the background and cached.
- Counters: per-client request and byte counts per minute, hour and day,
held in memory; the hour and day counts are written out so they survive a
restart.
- Attack detection: regex rules read at start from a directory of plain
text rule files (see "Rule files"), Coraza with the OWASP Core Rule Set,
and simple signals (requests for listed trap paths, bursts of error
responses from the app).
- Ban ledger: offences, active bans and ban history, held in memory and
written to disk as JSON (see "Persistent state"). No database of any kind
is used.
- Request log: one JSON object per request on stdout, optionally also sent
to a remote syslog or RELP endpoint (see "Request log").
- Metrics: Prometheus counters and gauges on their own listener (see
"Metrics endpoint").
- Alerting: a queue with de-duplication feeding webhook, Slack and ntfy
senders.
- Proxy: the standard library's `net/http/httputil.ReverseProxy`, streaming
in both directions, with WebSocket upgrade support.
- Proposed libraries (to be checked against the owner's Go dependency defaults
before any are added):
- standard library for the proxy, HTTP clients, DNS, logging (`log/slog`),
state files (`encoding/json`, `os.Rename`);
- `github.com/corazawaf/coraza/v3` and
`github.com/corazawaf/coraza-coreruleset` for attack detection;
- `github.com/oschwald/maxminddb-golang` to read `.mmdb` lookup databases;
- `github.com/prometheus/client_golang` for metrics;
- remote log sending: the standard library's `log/syslog` is frozen and
does not write the current syslog format (RFC 5424), and no widely used Go
RELP client was found, so the library for this is open (see Questions).
## Data flow for one request
Steps run in this order; the first step that produces a final answer ends
processing.
- Identify the client.
- If the TCP peer is inside `TRUSTED_PROXIES`, walk `X-Forwarded-For` from
the right and take the first address not inside `TRUSTED_PROXIES`.
Otherwise use the TCP peer address and ignore the header.
- IPv6 clients are grouped by prefix (`IPV6_GROUP_PREFIX`, default 64) for
counting and banning, because one abuser usually controls a whole /64.
- Static lists.
- In `ALLOW_NETS`: skip every check below and forward. Still counted for
anomaly alerts.
- In `DENY_NETS`: refuse.
- Ban ledger. An active ban: refuse (`BAN_RESPONSE`).
- Lookup AS number and country. Unknown is a valid result and changes nothing.
- Reputation.
- Address inside a fetched blocklist: apply `BLOCKLIST_ACTION`.
- Cached DNSBL or reputation API result: apply `REPUTATION_ACTION`.
- No cached result: queue a background query and carry on. A first request
is never delayed by a reputation query.
- Work out the client's limit percentage: the lowest of the percentages that
apply (AS number, country, reputation). 100 if none applies. 0 means refuse.
(Lowest-wins versus multiplying is open.)
- Request rate limits. Unless the client is in `RATE_LIMIT_EXEMPT_NETS`, check
the minute, hour and day counters against each configured limit times the
percentage. Over any limit: answer 429 with `Retry-After`, record an offence.
- Rule files. The request is checked against the rules loaded from
`RULES_DIR`, in file name order then line order. Each rule that matches takes
its action: record offences, refuse with 403, ban at once, or only log.
Matching stops at the first rule that refuses or bans.
- Core Rule Set inspection of the request (headers, URL, and body up to
`WAF_BODY_LIMIT`). In `block` mode a match at or over the anomaly threshold is
refused with 403 and recorded as an offence; in `detect` mode it is only
logged and alerted.
- Forward to `UPSTREAM_URL`, streaming. Add `X-Forwarded-For` and, if enabled,
`X-Client-ASN` and `X-Client-Country` for the app's own logs.
- After the response.
- Add response bytes (and request body bytes) to the byte counters. Once a
client's byte total passes a byte limit times the percentage, following
requests get 429 until the window moves on, and an offence is recorded. A
response already in progress is not cut off.
- Count 401, 403 and 404 responses from the app per client; passing
`ERROR_BURST_THRESHOLD` within a minute records an offence.
- Update anomaly counters and evaluate alert thresholds.
- Offences and bans.
- `BAN_AFTER_OFFENCES` offences within `OFFENCE_WINDOW` creates a ban.
- Ban length follows `BAN_DURATIONS` by the number of earlier bans for that
client within `BAN_HISTORY_WINDOW`: first ban the first value, second ban
the second value, and so on.
- After `PERMANENT_BAN_AFTER` bans within `BAN_HISTORY_WINDOW`, the ban has
no expiry.
- A request for a path in `TRAP_PATHS` counts as `TRAP_OFFENCE_WEIGHT`
offences at once.
## Counting method
- Each window (minute, hour, day) uses two adjacent fixed buckets per client,
with the previous bucket weighted by how much of it still overlaps the
sliding window. This costs a few integers per client per window and avoids
the burst at bucket boundaries that a single fixed bucket allows.
- Counters are read and updated in memory only. The hour and day counters are
written to disk on a timer and at shutdown and loaded again at start (see
"Persistent state"), so a restart does not hand every client a fresh daily
allowance. Minute counters are not written; a restart forgives at most one
minute of counting. Buckets whose time has passed are discarded on load.
- Memory is bounded by `MAX_TRACKED_CLIENTS`; when full, the least recently seen
clients with no recent offences are dropped first.
## Configuration surface
Conventions: lists are comma separated; netblocks are CIDR (a bare address means
/32 or /128); durations use Go syntax plus `d` for days (`90s`, `15m`, `24h`,
`7d`); byte sizes accept `K`, `M`, `G` suffixes; an unset limit means that
limit is off. Every variable may instead be given as `NAME_FILE` pointing at a
file holding the value, for secrets and long lists. Invalid configuration stops
the process at start with a message naming the variable. At start the effective
configuration is logged with secrets masked.
- Core
- `UPSTREAM_URL` (required): the application, for example
`http://gitea:3000`.
- `LISTEN_ADDR` (default `:8080`): proxy listener.
- `ADMIN_LISTEN_ADDR` (default `127.0.0.1:9090`): admin listener.
- `ADMIN_TOKEN`: bearer token required for ban management endpoints.
- `INSTANCE_NAME`: included in every log line, metric and alert, for example
`fsn1app1/gitea`.
- `MODE` (default `enforce`): `enforce`, or `observe` to log and alert on
every decision while refusing nothing. Meant for the first days of a
rollout.
- `TRUSTED_PROXIES` (required): netblocks whose `X-Forwarded-For` is
believed, normally the docker network traefik reaches the sidecar from.
- `IPV6_GROUP_PREFIX` (default `64`).
- `MAX_TRACKED_CLIENTS` (default `500000`).
- Persistent state
- `STATE_DIR` (default `/data`): the JSON state files and downloaded lookup
databases.
- `STATE_WRITE_DELAY` (default `2s`): after a ban or offence changes, wait
this long before writing, so a burst of changes becomes one write.
- `STATE_COUNTER_INTERVAL` (default `60s`): how often the hour and day
counters and the reputation cache are written.
- Logging
- The request log on stdout is always on and has no switch.
- `LOG_LEVEL` (default `info`): for the process's own messages (start-up,
fetch failures, state writes), which are JSON lines on stdout too, marked
`"type":"process"`. It does not filter the request log.
- `LOG_REQUEST_HEADERS` (default
`accept,accept-language,accept-encoding,content-type,origin,range`):
extra request headers to record. `Authorization`, `Cookie` and
`Set-Cookie` values are never logged, only whether they were present.
- `LOG_REMOTE_URL`: when set, every log line is also sent to this endpoint.
Forms: `syslog+udp://host:514`, `syslog+tcp://host:514`,
`syslog+tls://host:6514`, `relp://host:2514`, `relp+tls://host:2514`.
- `LOG_REMOTE_TLS_CA_FILE`: optional CA certificate for the `+tls` forms.
- `LOG_REMOTE_BUFFER` (default `10000`): lines held in memory while the
endpoint is unreachable; when full the oldest are dropped and counted.
- `LOG_REMOTE_FACILITY` (default `local0`), `LOG_REMOTE_APP_NAME` (default
`INSTANCE_NAME`): syslog header fields.
- Metrics
- `METRICS_ENABLED` (default `true`).
- `METRICS_LISTEN_ADDR` (default `:9100`): its own listener, so it can be
bound to a monitoring network without exposing the admin endpoints.
- `METRICS_PATH` (default `/metrics`).
- `METRICS_TOP_N` (default `50`): how many AS numbers and countries get
their own series; the rest are summed as `other`.
- `METRICS_TOKEN`: optional bearer token; unset means no authentication,
which is the usual arrangement for a scraper on a private network.
- Static lists
- `ALLOW_NETS`: bypass everything (monitoring, the owner's own networks).
- `RATE_LIMIT_EXEMPT_NETS`: bypass request and byte limits only; attack
detection and bans still apply.
- `DENY_NETS`: always refused.
- Request rate limits, per client (R1, R2)
- `RATE_LIMIT_PER_MINUTE`, `RATE_LIMIT_PER_HOUR`, `RATE_LIMIT_PER_DAY`.
- `RATE_LIMIT_EXEMPT_PATHS`: path prefixes not counted (static assets,
health checks).
- Byte limits, per client
- `BYTES_LIMIT_PER_MINUTE`, `BYTES_LIMIT_PER_HOUR`, `BYTES_LIMIT_PER_DAY`.
- `BYTES_COUNT` (default `both`): `response`, `request` or `both`.
- Lookup of AS number and country (R7)
- `ASN_DB_PATH`, `COUNTRY_DB_PATH`: `.mmdb` files mounted into the
container; or
- `ASN_DB_URL`, `COUNTRY_DB_URL`: downloaded into `STATE_DIR` at start and
every `LOOKUP_DB_REFRESH` (default `7d`). One file may serve both.
- Known free sources in this format: IPinfo Lite (country and AS number in
one file, free account token), DB-IP Lite, MaxMind GeoLite2 (free
account). Choice is open.
- `ADD_LOOKUP_HEADERS` (default `false`): pass `X-Client-ASN` and
`X-Client-Country` to the app.
- Missing or unreadable database: start anyway, treat every client as
unknown, log a warning and send one alert.
- Biased thresholds (R8)
- `ASN_LIMIT_PERCENT`: for example `AS14061:50,AS16276:50,AS45102:25`.
Listed AS numbers get that percentage of every request and byte limit.
`0` refuses outright.
- `COUNTRY_LIMIT_PERCENT`: same form with ISO country codes, for example
`CN:25,RU:50`.
- `ASN_BYTES_PERCENT`, `COUNTRY_BYTES_PERCENT`: optional overrides applied
to byte limits only, when the byte percentage should differ from the
request percentage.
- `UNKNOWN_LIMIT_PERCENT` (default `100`): for clients the lookup cannot
place.
- `ASN_LIMIT_PERCENT_URL`: optional URL of a text file of `AS:percent`
lines, so one abuse-source list can be shared by every sidecar in the
fleet.
- Attack detection (R9)
- `RULES_DIR` (default `/etc/smallwebwaf/rules.d`): directory of rule files
read once at start; format under "Rule files". The image ships a default
file there. Mounting a directory over it replaces the defaults; mounting
single files into it adds to them.
- `RULES_ENABLED` (default `true`): `false` skips rule files entirely.
- `WAF_MODE` (default `detect`): `off`, `detect`, `block`.
- `WAF_PARANOIA_LEVEL` (default `1`), `WAF_ANOMALY_THRESHOLD` (default `5`):
the Core Rule Set's own two tuning values.
- `WAF_DISABLED_RULES`: rule ids to switch off when an app trips a false
positive.
- `WAF_EXEMPT_PATHS`: path prefixes not inspected.
- `WAF_BODY_LIMIT` (default `128K`): bodies are inspected up to this size
and streamed beyond it without buffering, so large uploads and git pushes
are not held in memory.
- `TRAP_PATHS`: paths the app never serves and only scanners ask for, for
example `/.env,/wp-login.php,/.git/config`. `TRAP_OFFENCE_WEIGHT`
(default `3`). This is the env-var short form of a `path` rule with an
`offence` action, for deployments that mount no rule files.
- `ERROR_BURST_THRESHOLD` (default off): 401, 403 and 404 responses per
client per minute that count as an offence.
- Blocks and bans (R5)
- `BAN_AFTER_OFFENCES` (default `3`), `OFFENCE_WINDOW` (default `10m`).
- `BAN_DURATIONS` (default `1h,24h,7d`).
- `PERMANENT_BAN_AFTER` (default `4`; `0` never bans permanently),
`BAN_HISTORY_WINDOW` (default `90d`).
- `BAN_RESPONSE` (default `403`): `403`, `429`, or `close` to drop the
connection without an answer.
- `BAN_SCOPE_V4_PREFIX` (default `32`): widen to for example `24` to ban the
surrounding netblock.
- Reputation (R6)
- `BLOCKLIST_URLS`: text files of addresses and netblocks, for example
Spamhaus DROP, FireHOL level 1, the Tor exit list. Refreshed every
`BLOCKLIST_REFRESH` (default `6h`); the last good copy is kept on failure.
- `BLOCKLIST_ACTION` (default `limit:25`): `deny`, `limit:<percent>`, or
`log`.
- `DNSBL_ZONES`: for example `dnsbl.dronebl.org`. Zones meant for mail
(lists of residential ranges) will block ordinary visitors and should not
be used; Spamhaus zones need their keyed query service, given as a zone
name containing the key.
- `DNSBL_RESOLVER`: optional resolver address, since public resolvers are
refused by several list operators.
- `ABUSEIPDB_KEY`, `ABUSEIPDB_MIN_SCORE` (default `75`),
`ABUSEIPDB_DAILY_BUDGET` (default `900`; the free tier allows 1000 checks
a day). Only clients that have already committed one offence are queried,
so the budget is spent on suspects.
- `CROWDSEC_LAPI_URL`, `CROWDSEC_LAPI_KEY`: optional. If a CrowdSec engine
exists on the host, pull its decision list on a schedule and treat listed
addresses as banned. This is how a fleet-wide blocklist can arrive
without the sidecar depending on CrowdSec.
- `REPUTATION_ACTION` (default `limit:25`): `deny`, `limit:<percent>`, or
`log`, for DNSBL and API hits.
- `REPUTATION_CACHE_TTL` (default `24h`), `REPUTATION_TIMEOUT` (default
`2s`).
- Alerting (R3)
- `ALERT_WEBHOOK_URL`: JSON POST; schema below.
`ALERT_WEBHOOK_HEADERS`: optional `Name:value` pairs for authentication.
- `ALERT_SLACK_WEBHOOK_URL`: Slack incoming webhook, formatted message.
- `ALERT_NTFY_URL` (full topic URL), `ALERT_NTFY_TOKEN`: title, priority
and tags set from the event type.
- `ALERT_EVENTS` (default
`ban,permanent_ban,waf_block,anomaly,reputation_hit,source_failure`):
which event types are sent.
- `ALERT_COOLDOWN` (default `15m`): the same event type for the same client
or netblock is not repeated within this time; a count of suppressed
repeats is included in the next one.
- `ALERT_MAX_PER_HOUR` (default `60`): beyond this, alerts are rolled into
one summary per hour so a wide attack cannot flood the channel.
- Anomaly thresholds, alert only, nothing is blocked (R4)
- Per client: `ANOMALY_CLIENT_REQUESTS_PER_MINUTE`,
`ANOMALY_CLIENT_REQUESTS_PER_HOUR`, `ANOMALY_CLIENT_BYTES_PER_MINUTE`,
`ANOMALY_CLIENT_BYTES_PER_HOUR`.
- Per surrounding netblock (`ANOMALY_NET_V4_PREFIX` default `24`,
`ANOMALY_NET_V6_PREFIX` default `48`): `ANOMALY_NET_REQUESTS_PER_MINUTE`,
`..._PER_HOUR`, `ANOMALY_NET_BYTES_PER_MINUTE`, `..._PER_HOUR`.
- Per AS number: `ANOMALY_ASN_REQUESTS_PER_MINUTE`, `..._PER_HOUR`,
`ANOMALY_ASN_BYTES_PER_MINUTE`, `..._PER_HOUR`.
- Whole service: `ANOMALY_TOTAL_REQUESTS_PER_MINUTE`, `..._PER_HOUR`,
`ANOMALY_TOTAL_BYTES_PER_MINUTE`, `..._PER_HOUR`.
- Named netblocks: `WATCH_NETS`, for example
`office=203.0.113.0/24,scraper-x=198.51.100.0/22`, with
`WATCH_REQUESTS_PER_MINUTE`, `..._PER_HOUR`, `WATCH_BYTES_PER_MINUTE`,
`..._PER_HOUR` applied to each named block as a whole.
- Anomaly counting includes clients in `ALLOW_NETS` and
`RATE_LIMIT_EXEMPT_NETS`, since an exempt client misbehaving is worth
knowing about.
## Rule files
A required feature: at start the sidecar reads every `*.rules` file in
`RULES_DIR` and checks each request against them. The files are plain text meant
to be edited by hand, so that a new scanning pattern seen in the request log can
be turned into a rule in one line.
- One rule per line, four fields separated by spaces or tabs; the fourth field
runs to the end of the line:
```
<id> <target> <action> <regex>
```
- Blank lines and lines starting with `#` are ignored.
- `id`: a short name of letters, digits, `-` and `_`, unique across all files.
It appears in the request log, metrics, alerts and offence history.
- `target`: what the regex is matched against.
- `path`: the URL path as received, before any decoding.
- `query`: the raw query string.
- `uri`: path and query together, both as received and once
percent-decoded, so an encoded probe cannot slip past.
- `method`, `host`, `user_agent`, `referer`.
- `header:<Name>`: any one request header.
- Request bodies are not available to rule files; body inspection is the
Core Rule Set's job.
- `action`:
- `log`: note the match in the request log and do nothing else.
- `offence` or `offence:<n>`: record one or `n` offences and forward the
request. Enough offences within `OFFENCE_WINDOW` creates a ban.
- `block` or `block:<n>`: refuse with 403 and record one or `n` offences.
- `ban`: refuse and ban the client at once, at whatever length its ban
history calls for.
- `regex`: Go regular expression syntax (RE2). It has no backreferences or
lookaround, and in exchange matching time is linear in the input, so no rule
can be made to stall the proxy. `(?i)` at the front makes a rule
case-insensitive. A rule matches if the regex matches anywhere in the target;
anchor with `^` and `$` when that is not wanted.
- Files are read in name order (`00-default.rules` before `50-gitea.rules`),
rules in line order.
- Rules are compiled once at start and held in memory. A line that does not
parse, a regex that does not compile, or a duplicate id stops the process
with a message naming the file and line. A missing or empty directory is not
an error: the log says that no rules were loaded. Changing rules means
restarting the container; reloading while running is given up for now.
- In `MODE=observe` every action is logged as what would have happened and
nothing is refused.
- Clients in `ALLOW_NETS` are not checked.
Example file:
```
# 00-default.rules: probes no real visitor sends
# id target action regex
env-file path offence:3 (?i)/\.env(\.[a-z]+)?$
git-dir path offence:3 ^/\.git/(config|HEAD|index)$
wp-probe path offence:3 (?i)^/(wp-login\.php|xmlrpc\.php|wp-admin/)
php-shell path block:3 (?i)/(shell|c99|r57|wso|alfa)\.php$
path-traversal uri block (\.\./){2,}
scanner-agent user_agent ban (?i)\b(sqlmap|nikto|nuclei|masscan|zgrab|wpscan)\b
empty-agent user_agent log ^$
```
The image ships one default file of this kind. It is kept short and limited to
patterns that are wrong for every app; anything app-specific (for example
blocking `/wp-login.php` is harmless in front of gitea and fatal in front of
WordPress) belongs in a file the deployer mounts.
## Persistent state
All state lives in memory. No database is used. What must survive a restart is
written to `STATE_DIR` as JSON files; the files are read once at start and never
during a request. The whole state is expected to stay under 10 MiB, and reading
or writing even ten times that as JSON takes well under a second, so whole-file
rewrites are cheap enough to need nothing cleverer.
- Files, each holding one kind of state:
- `bans.json`: active and past bans. Per entry: client or netblock, start,
expiry (`null` for permanent), reason, which ban this is for that client
(first, second, third), source (`local`, `admin`, `crowdsec`), and when
it was lifted, if it was.
- `offences.json`: offender history. Per entry: client, time, kind (`rate`,
`bytes`, `waf`, `trap`, `error_burst`), short detail. Entries older than
`BAN_HISTORY_WINDOW` are dropped at each write.
- `counters.json`: the hour and day request and byte counters per client.
- `reputation.json`: cached DNSBL and reputation API verdicts with the time
each was fetched.
- Format: indented JSON with a top-level `version` number, entries sorted by
client address, times in RFC 3339 UTC, durations and sizes as plain numbers
with the unit in the field name. The aim is that a person can open
`bans.json` in an editor, find an address, and remove or add an entry.
- Writing:
- serialise from a snapshot taken under the lock, so requests are not held
up while the file is written;
- write to a temporary file in the same directory, sync it, rename it over
the real name, sync the directory. A crash at any point leaves either the
old complete file or the new complete file, never a partial one;
- `bans.json` and `offences.json` are written `STATE_WRITE_DELAY` after a
change; `counters.json` and `reputation.json` every
`STATE_COUNTER_INTERVAL`; all four on orderly shutdown (SIGTERM).
- Reading:
- at start only. Active bans go into an in-memory prefix lookup; everything
else into maps. Expired counters and cache entries are discarded.
- a missing file means empty state and is normal on first run.
- a file that does not parse, or has an unknown `version`, stops the
process with a message naming the file and position. Starting with empty
bans would silently forgive every repeat offender, and since writes are
atomic a broken file can only come from a hand edit, which the editor
should hear about. `counters.json` and `reputation.json` are the
exception: if unreadable they are logged, set aside with a `.bad` suffix,
and the process starts with them empty.
- Hand edits are made with the container stopped; a running process will
overwrite the file at its next write. Changes to a running process go through
the admin endpoints. Reloading files into a running process is given up for
now.
- `STATE_DIR` not writable at start: the process exits. A write that fails
while running: state stays correct in memory, the failure is logged, counted
in metrics, alerted once per cooldown, and retried at the next write.
- What a hard kill can lose: bans and offences from the last
`STATE_WRITE_DELAY`, counters from the last `STATE_COUNTER_INTERVAL`. Losing
the volume loses ban history, not service.
## Request log
One JSON object per line on stdout for every request, including refused ones.
stdout is always on. When `LOG_REMOTE_URL` is set the same lines are also sent
to the remote endpoint, so a deployment can stop depending on docker's log
handling while `docker logs` keeps working.
- Standard web log fields: `time` (RFC 3339 with milliseconds), `instance`,
`client_ip`, `method`, `scheme`, `host`, `path`, `query`, `protocol`,
`status`, `request_bytes`, `response_bytes`, `referer`, `user_agent`.
- Request detail: `request_id` (generated if traefik did not supply one, and
passed to the app), `peer_ip` (the TCP peer, normally traefik),
`forwarded_for` (the header as received), `client_group` (the /64 or
configured prefix used for counting), `asn`, `as_name`, `country`,
`content_type`, `content_length`, the headers named in
`LOG_REQUEST_HEADERS`, `has_authorization` and `has_cookie` as booleans,
`websocket` when the connection was upgraded.
- Response detail: `response_content_type`, `upstream_status` (differs from
`status` when the sidecar answered itself), `cache_control`, `location` on
redirects, `aborted` when the client went away early.
- Decision: `action` (`forward`, `rate_limited`, `bytes_limited`, `banned`,
`denied`, `waf_blocked`, `upstream_error`), `would_action` in `observe` mode,
`limit_percent` and which rule set it, `counts` (the client's minute, hour
and day request and byte totals after this request), `limit_hit` (which
window), `rule_ids` (rule file rules that matched), `waf_rule_ids`,
`waf_score`, `reputation` (sources that listed the
client), `offence` when one was recorded, `ban_expires`.
- Timings in milliseconds: `duration_total`, `duration_checks` (everything the
sidecar did before forwarding), `duration_waf`, `duration_upstream_connect`,
`duration_upstream_first_byte`, `duration_upstream_total`.
- Bodies are never logged. Query strings are logged as received; an app that
carries secrets in query strings needs that fixed in the app.
- The process's own messages share the stream as JSON lines with
`"type":"process"`; request lines carry `"type":"request"`.
- Remote sending:
- syslog forms send each line as the message of an RFC 5424 record, with
octet-counted framing on TCP and TLS;
- RELP forms send the same record and wait for the receiver's
acknowledgement, so lines are not lost across a receiver restart. This is
the form to use with rsyslog;
- sending happens on its own goroutine from a bounded buffer
(`LOG_REMOTE_BUFFER`). An unreachable or slow endpoint never delays a
request and never stops stdout; it reconnects with backoff, drops the
oldest lines when the buffer is full, and counts the drops in metrics.
UDP gives no delivery signal at all and is offered only for
compatibility.
## Metrics endpoint
Prometheus text format on `METRICS_LISTEN_ADDR` at `METRICS_PATH`, on by default,
switched off with `METRICS_ENABLED=false`. It has its own listener so it can be
reached by a scraper without exposing ban management.
- Traffic: requests and bytes in and out, by status class and `action`;
request duration and upstream duration histograms; requests in flight.
- Limits and bans: limit hits by window and kind (requests or bytes), offences
by kind, bans created by ordinal, permanent bans, active bans (gauge).
- Attack detection: rule file matches by rule id and action, and the number of
rules loaded; Core Rule Set matches by mode and rule id (label limited to the
rules that actually fired).
- Lookup and reputation: requests and bytes by AS number and by country, limited
to the `METRICS_TOP_N` (default `50`) busiest of each with the rest summed as
`other`, so the label set stays bounded; reputation queries, hits, failures
and remaining daily budget by source; age of each blocklist and lookup
database.
- Housekeeping: tracked clients (gauge), state file writes, write failures,
last successful write time and size per file; alerts sent, failed and
suppressed by destination; remote log lines sent, dropped and buffer depth;
the standard Go runtime and process metrics.
- No metric carries a client IP address as a label; per-address questions are
answered by the request log and `GET /clients/<ip>`.
## Admin listener
- `GET /healthz`: for the container health check.
- `GET /bans`, `POST /bans` (client or netblock, duration, reason),
`DELETE /bans/<client>`: need `ADMIN_TOKEN`.
- `GET /clients/<ip>`: current counters, lookup result, reputation, offences;
for answering "why was this address refused".
## Alert webhook schema
One JSON object per alert:
- `instance`, `time`, `event` (one of the `ALERT_EVENTS` values)
- `client`, `netblock`, `asn`, `as_name`, `country`
- `reason`: short human-readable sentence
- `detail`: event-specific fields, for example `window`, `count`, `limit`,
`limit_percent`, `rule_ids`, `path`, `ban_ordinal`, `ban_expires`
- `suppressed_repeats`: number of identical alerts held back by the cooldown
## Deployment as a sidecar
docker-compose shape, using gitea as the example; upaas deployments follow the
same shape if upaas can run a second container for a service (open):
```yaml
services:
gitea:
image: gitea/gitea:1
# no traefik labels, no published ports
networks: [internal]
gitea-guard:
image: <registry>/<image>:<pinned digest>
read_only: true
user: "65532:65532"
environment:
UPSTREAM_URL: http://gitea:3000
TRUSTED_PROXIES: 172.18.0.0/16
INSTANCE_NAME: fsn1app1/gitea
MODE: observe
RATE_LIMIT_PER_MINUTE: "120"
RATE_LIMIT_PER_HOUR: "2000"
RATE_LIMIT_PER_DAY: "10000"
BYTES_LIMIT_PER_HOUR: 2G
ASN_DB_URL: https://example.invalid/asn-country.mmdb
ASN_LIMIT_PERCENT: AS14061:50,AS16276:50
COUNTRY_LIMIT_PERCENT: CN:25
WAF_MODE: detect
TRAP_PATHS: /.env,/wp-login.php,/.git/config
BLOCKLIST_URLS: https://www.spamhaus.org/drop/drop.txt
ALERT_NTFY_URL: https://ntfy.example.invalid/fleet-alerts
LOG_REMOTE_URL: relp://logs.example.invalid:2514
METRICS_LISTEN_ADDR: :9100
volumes:
- gitea-guard-state:/data
- ./50-gitea.rules:/etc/smallwebwaf/rules.d/50-gitea.rules:ro
networks: [internal, traefik]
labels:
traefik.enable: "true"
traefik.http.routers.gitea.rule: Host(`git.example.invalid`)
traefik.http.services.gitea.loadbalancer.server.port: "8080"
```
- The application container leaves the traefik network, so the sidecar cannot
be bypassed.
- Traefik routes only port 8080. The metrics port is reached by the scraper
over a docker network it shares with the sidecar; the admin port stays on
loopback inside the container and is used through `docker exec`.
- The state volume holds a few small JSON files; it needs no backup beyond
whatever the host already does.
- SSH access to gitea does not pass through the sidecar and is not protected
by it.
- Rollout per service: start in `MODE=observe` with `WAF_MODE=detect`, read a
few days of logs and alerts, set limits and rule exclusions from what real
traffic looks like, then switch to `enforce` and `block`.
- Notes specific to gitea: clones and pushes over HTTP are large and long, so
byte limits must be sized for a legitimate clone, the proxy sets no overall
response timeout, and `WAF_BODY_LIMIT` keeps pack uploads out of memory.
Archive download and blame or history pages are what scrapers hammer; request
limits do most of the work there.
## Failure behaviour
- Lookup database missing: clients are unknown, service continues, one alert.
- Reputation source down or over quota: no verdict, service continues, one
`source_failure` alert per cooldown.
- Alert destination down: retried with backoff from a bounded queue, oldest
dropped first, drops counted in metrics.
- Upstream down: 502 from the sidecar, not counted as client offences.
- Attack detection engine error on a request: request is forwarded, error
logged and counted.
- Remote log endpoint down: stdout continues, lines are buffered then dropped
oldest first, drops counted in metrics.
- State file write fails while running: memory stays authoritative, logged,
counted, alerted, retried.
- In short: the only things that stop the process are invalid configuration,
a rule file that does not parse, an unwritable `STATE_DIR`, and an unparseable `bans.json` or `offences.json`
at start. A broken helper never takes the protected service down.
## Risks the design has to handle
- Forged `X-Forwarded-For`: handled by `TRUSTED_PROXIES` being required and by
walking the header from the right.
- Many clients behind one address (mobile carriers, offices, Tor): rate limits
punish them collectively; `RATE_LIMIT_EXEMPT_NETS` and sensible day limits
are the remedy, and bans on such addresses should stay short.
- IPv6 address rotation inside a /64: handled by grouping.
- Widely distributed scrapers using thousands of addresses at low rates each:
per-client limits do not see them. The AS number and netblock anomaly
alerts reveal them, and `ASN_LIMIT_PERCENT` at a low value or `0` is the
response. A per-AS-number or per-country total limit is open.
- Core Rule Set false positives against real apps (gitea's editor, API
payloads): `detect` by default, exclusions by rule id and path.
- Slow-request attacks: header read timeout and idle timeout on the listener.
- Alert floods: cooldown and hourly cap.
## Build order
- First: proxy, client identification, static lists, three-window request
limits, exemptions, `observe` mode, the full request log on stdout, the
metrics endpoint, health.
- Second: rule files, ban ledger with escalation and permanent bans, the JSON
state files,
admin endpoints, alerting to all three destinations, remote log sending.
- Third: AS number and country lookup, biased thresholds, byte limits, anomaly
thresholds.
- Fourth: blocklists, DNSBL, AbuseIPDB, optional CrowdSec decision feed.
- Fifth: attack detection with Coraza and the Core Rule Set, trap paths, error
bursts.
- Each stage is usable on its own; the first three already cover the traffic
problem the fleet has today.
## Questions for the owner
- Combining percentages. A client in a listed AS number (50 percent) and a
listed country (25 percent): should it get the lowest (25 percent of the
normal limit) or the product (12.5 percent)? Lowest is easier to predict when
reading a config; product punishes overlap harder. Recommendation: lowest.
- Meaning of "certain countries getting a percentage rate or byte limit". Read
here as: each client from that country gets that percentage of the normal
per-client limits. The other reading is a cap on the country as a whole, for
example all of one country together may use at most 20 percent of the
service's hourly byte budget. The second needs a configured total budget and
means one heavy client can lock out its compatriots. Recommendation: build
the per-client reading first; add whole-country and whole-AS-number caps only
if distributed scrapers make it necessary.
- Sharing bans across the fleet. As drafted, each sidecar remembers only its
own bans, so an abuser banned at gitea starts fresh at the next service.
Options: keep it per sidecar; or run one CrowdSec engine per host and have
every sidecar read its decision list (already supported above) and also
report its own bans to it. Recommendation: per sidecar for the first version,
decide on CrowdSec after seeing real ban volumes.
- Lookup database source. IPinfo Lite (one file with country and AS number,
free account, attribution required), DB-IP Lite (no account, attribution
required), or MaxMind GeoLite2 (free account, licence terms on
redistribution). Recommendation: IPinfo Lite, fetched once centrally and
served to the fleet from an internal URL so sidecars hold no account token.
- upaas. Whether upaas can deploy a second container beside an app and move
the traefik labels onto it was not examined. If it cannot, that is a feature
request for upaas, not something this sidecar can solve.
- Remote log library. Sending syslog in the current format (RFC 5424) is not
covered by Go's standard library, whose `log/syslog` package is frozen and
writes the older format, and no widely used Go RELP client was found. The
choices are a small third-party package for each, or writing both inside this
project; the syslog record is a few dozen lines, a RELP client with
acknowledgement handling is a few hundred. Recommendation: write the syslog
sender in-project, ship it first, and decide on RELP after looking at the
available packages; say if RELP must be in the first release.
- Ban response. `403` tells the abuser they were noticed; `close` wastes less
and tells them nothing. Recommendation: `403` by default for debuggability,
`close` available.