alerting: Signal via signal-cli-rest-api, and faster failure detection
Three changes: detection windows tightened, a Signal transport deployed, and
alerts attached to all 84 non-transport endpoints.
── Failing faster ──────────────────────────────────────────────────────────
The heartbeat is a TICKER, not a deadline: Gatus wakes every interval and asks
"did anything arrive in the last interval", so real detection is 1-2x the
window. And a window can only ever be as tight as the push frequency - which is
why two checks moved rather than just having their numbers changed.
liveness, cpu, ups, service-health, probes 16m -> 11m
disk, zfs daily/30h -> 6-hourly/7h
backup store + pull job daily/30h -> 6-hourly/7h
DNS records 24h -> 6h
backup dump 30h -> 26h
backup-dump stays slow because the dump genuinely is daily. The store-side check
catches the same fault within 6h by reading the source's dump timestamp out of
the artefact filename, so 26h is a backstop rather than the primary signal.
── Thresholds differ by check type, deliberately ───────────────────────────
`failure-threshold` counts consecutive failures, but "consecutive" is a
different amount of wall-clock time per check: a push endpoint produces one
failure per heartbeat window, a pulled one per interval. The default of 3 would
mean 33 minutes on an 11m heartbeat and over a day on a 7h one.
More importantly the heartbeat window ALREADY encodes the tolerance - an 11m
window on a 5-minute push is exactly "one missed push forgiven" - so stacking a
threshold of 3 triples a tolerance that was already chosen. Hence:
push/heartbeat endpoints failure-threshold 1
pulled, 5m (public) failure-threshold 3 (= 15 minutes)
pulled, 6h/24h (dns, domain) failure-threshold 1
── The Signal transport ────────────────────────────────────────────────────
roles/signal_api runs signal-cli-rest-api on the observability host, pinned by
digest, MODE=native.
It publishes NO PORTS. The API has no authentication of any kind - anything that
reaches it can send messages as you and read your Signal. Gatus talks to it over
a shared docker network by service name, which is also WHY the network exists:
Gatus runs in a container, so the host's loopback is unreachable from it and a
port published on 127.0.0.1 would not have worked.
MODE=native and not json-rpc because this VPS has 464MB of RAM and already runs
Gatus and Caddy. The json-rpc modes hold a resident JVM; native runs a binary
per request, and alerts are rare enough that startup cost per alert is the right
trade.
Monitored - Gatus polls /v1/health over the same network path the alerts take,
so it proves the delivery route rather than mere container liveness. Deliberately
NOT backed up: the data directory holds Signal private keys and the recovery
path is to link the device again from the phone.
Neither the signal-api endpoint nor Gatus's self-check carries a Signal alert.
If either is down, Signal is precisely what cannot deliver the alert.
── Four traps hit while linking, all now in the role README ────────────────
* /v1/qrcodelink is BROKEN in native mode - returns "no data to encode" while
the binary itself emits a perfectly good URI. Not worked around by switching
MODE, which would put a JVM in the path of every alert permanently.
* The data dir must be owned by uid 1000, not root. A root-owned 0700 dir
cannot be traversed by the container user, so linking silently never
completes and /v1/accounts returns "Failed to read local accounts list".
* `docker exec` runs as ROOT while the service runs as uid 1000, so without
--config the account is written to /root/... on the container's ephemeral
layer. It reports success and is destroyed on the next recreate.
* The phone reporting "network error" was IPv6: chat.signal.org resolves to
dualstack AAAA records first, the container has no IPv6 address, and this
host's IPv6 path is broken - the same edge that 404'd the Go tarball. Fixed
with a mounted gai.conf that prefers IPv4.
Verified: provider loads (configuredProviders=[signal]), a test message was
delivered and confirmed received, 84 endpoints carry alerts, 86 UP / 0 DOWN.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
This commit is contained in:
parent
85040d5f67
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20 changed files with 752 additions and 181 deletions
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@ -75,23 +75,36 @@
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'group': 'domain',
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'url': 'https://' ~ item,
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'interval': '24h',
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'conditions': ['[DOMAIN_EXPIRATION] > 336h']}] }}"
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'conditions': ['[DOMAIN_EXPIRATION] > 336h'],
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'alerts': [{'type': 'signal', 'failure-threshold': 1,
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'success-threshold': 1, 'send-on-resolved': true,
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'minimum-reminder-interval': '168h'}]}] }}"
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loop: "{{ monitored_domains }}"
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# ── DNS ──────────────────────────────────────────────────────────────────
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# 6h, not daily: a DNS query is cheap and a wrong record is an outage. The
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# domain check stays at 24h because it does a WHOIS/RDAP lookup against a
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# free service. Alert on the first failure - at a 6h interval, waiting for
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# three would be nearly a day.
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- name: Build the DNS endpoints
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ansible.builtin.set_fact:
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dns_endpoints: "{{ dns_endpoints | default([]) + [{
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'name': item.sub ~ '.' ~ root_domain,
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'group': 'dns',
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'url': dns_resolver,
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'interval': '24h',
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'interval': '6h',
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'dns': {'query-type': 'A', 'query-name': item.sub ~ '.' ~ root_domain},
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'conditions': ['[DNS_RCODE] == NOERROR',
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'[BODY] == ' ~ hostvars[item.host].ansible_host]}] }}"
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'[BODY] == ' ~ hostvars[item.host].ansible_host],
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'alerts': [{'type': 'signal', 'failure-threshold': 1,
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'success-threshold': 1, 'send-on-resolved': true,
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'minimum-reminder-interval': '24h'}]}] }}"
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loop: "{{ dns_records }}"
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# ── Public HTTP ──────────────────────────────────────────────────────────
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# failure-threshold 3 at a 5m interval = 15 minutes. A pulled endpoint has
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# no heartbeat window, so unlike the push checks the tolerance has to live
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# in the threshold - and one failed poll of a public site is usually a blip.
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- name: Build the public HTTP endpoints
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ansible.builtin.set_fact:
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http_endpoints: "{{ http_endpoints | default([]) + [{
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@ -100,7 +113,10 @@
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'url': 'https://' ~ item.sub ~ '.' ~ root_domain ~ item.path,
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'interval': '5m',
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'conditions': ['[STATUS] == ' ~ item.status,
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'[CERTIFICATE_EXPIRATION] > 168h']}] }}"
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'[CERTIFICATE_EXPIRATION] > 168h'],
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'alerts': [{'type': 'signal', 'failure-threshold': 3,
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'success-threshold': 2, 'send-on-resolved': true,
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'minimum-reminder-interval': '6h'}]}] }}"
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loop: "{{ public_sites }}"
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# ── Public TCP ───────────────────────────────────────────────────────────
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@ -111,7 +127,10 @@
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'group': 'public',
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'url': 'tcp://' ~ hostvars[item.host].ansible_host ~ ':' ~ item.port,
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'interval': '5m',
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'conditions': ['[CONNECTED] == true']}] }}"
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'conditions': ['[CONNECTED] == true'],
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'alerts': [{'type': 'signal', 'failure-threshold': 3,
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'success-threshold': 2, 'send-on-resolved': true,
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'minimum-reminder-interval': '6h'}]}] }}"
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loop: "{{ public_tcp }}"
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- name: Register the public-facing endpoints
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