StasonJatham
e8f7d6bfdf
Single stateless Go process that consumes CT logs via embedded (patched) CertSpotter internals, classifies cloud/database/storage DNS identifiers in-process with a zero-allocation classifier, enriches via round-robin DNS resolvers with CNAME following, and batch-writes useful findings to PostgreSQL. - third_party/certspotter: 2-hunk IdentifierSink patch, no stdout/JSON/files - internal/classify: AWS/Azure/GCP/Firebase/Cloudflare R2/DigitalOcean/Supabase/OCI - internal/dns: sharded bounded TTL cache, multi-resolver load balancing + failover - internal/pipeline: bounded queues, dedup, direct-priority load shedding - internal/store: pgx batch writer, Postgres CT checkpoints (no cert contents) - internal/probe: optional non-destructive reachability checks (off by default) - Docker: distroless non-root, read-only rootfs, no app volume, resource limits - tests enforce 0 allocs/op on the classifier and sink hot path
93 lines
3.8 KiB
Markdown
93 lines
3.8 KiB
Markdown
# Architecture
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## Data flow
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```text
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Certificate Transparency Logs
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│
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▼
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CertSpotter internals fetch / verify / parse (third_party)
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(in-process, no stdout/JSON/files)
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│
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▼
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DNS identifiers
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│
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▼
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FAST CLASSIFIER 0 allocs/op, no regexp/JSON/DNS/DB
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┌────┴─────┐
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direct cloud normal
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resource hostname
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│ │
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│ ▼
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│ DNS/CNAME enrichment bounded workers + TTL cache
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│ │
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│ ▼
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│ classify CNAME targets
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│ │
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└─────┬──────┘
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▼
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dedup/enrichment TTL caches; DB uniqueness is final
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│
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▼
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optional safe reachability HTTPS GET / only, OFF by default
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▼
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batch DB writer bounded queue, pgx batches
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▼
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PostgreSQL
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```
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## Stages and what is allowed
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| Stage | May do | Must not do |
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| --- | --- | --- |
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| CertSpotter fetch/verify/parse | network, crypto, in-memory DER | persist certs, write files |
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| Identifier callback | iterate `DNSNames`, call classifier | block, log per certificate, allocate needlessly |
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| Classifier | byte/string comparisons, label scan | regexp, JSON, reflection, DNS, HTTP, DB, files, per-id logging |
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| Direct queue | bound, non-blocking send | unbounded growth |
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| DNS enrichment | DNS via worker pool, TTL cache, CNAME follow | unbounded goroutines, persistence |
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| Dedup | memory-bounded TTL caches | unbounded maps |
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| Probe (optional) | DNS/TCP/TLS/HTTP HEAD/GET `/` | auth, downloads, mutation, DB or shell access |
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| DB writer | batched `pgx.Batch` writes | one synchronous row per event |
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| Checkpoints | JSON CT position in `ct_checkpoints`/`ct_sths` | certificate/issuer contents in DB |
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## Concurrency and backpressure
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* CertSpotter runs one monitor goroutine per CT log; it calls the identifier
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sink concurrently.
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* The sink never blocks: it classifies inline and does a non-blocking send to
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either the direct queue or the DNS queue. Full queues increment
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`queue_drops_total` / `queue_full_total`.
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* Direct matches have a dedicated queue and worker pool, so speculative CNAME
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enrichment can be shed first. DNS workers also skip work when the DB queue is
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more than half full.
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* The DB writer batches by size or `DB_FLUSH_INTERVAL` and flushes on
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shutdown.
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## Failure handling
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* DNS and CT network errors are retried by CertSpotter with bounded exponential
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backoff; ctcloud counts them (`ct_errors_total`) without logging per event.
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* PostgreSQL writes retry a few times with backoff; persistent failure drops
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items from the bounded DB queue rather than growing memory.
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* The process uses `context` throughout and on `SIGTERM` stops intake, drains
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the pipeline, flushes the DB batch and exits within `SHUTDOWN_TIMEOUT`.
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## Metrics and health
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`GET /metrics` exposes counters (`ct_certificates_total`,
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`classifier_direct_matches_total`, `classifier_cname_matches_total`,
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`dns_*`, `db_*`, `queue_*`) and gauges (`queue_depth{queue="…"}`,
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`go_goroutines`, `process_system_bytes`). No hostnames or other high-cardinality
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labels are ever used.
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`GET /healthz` is a liveness check. `GET /readyz` verifies the CT monitor is
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initialised and PostgreSQL is reachable.
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## Why no files, pipes or subprocesses
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Everything between certificate parsing and classification stays in memory. The
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CertSpotter patch hands identifiers directly to Go code, removing serialization
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(JSON), IPC (stdout/pipe), process boundaries (subprocess/hooks) and filesystem
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I/O (certificate/state files). CT resume state is the only thing persisted, and
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it lives in PostgreSQL.
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