{
  "port": 9009,
  "protocol": "tcp",
  "service": "ClickHouse interserver replication",
  "oneLiner": "ClickHouse's server-to-server port: replicas fetch data parts from each other here.",
  "whatItIs": "ClickHouse uses 9009 for inter-server communication — replication and data exchange between replicas at the low-level data access layer — separate from the 9000 native client protocol and the 8123 HTTP interface. On a ClickHouse cluster every node has it open to its peers. IANA registers 9009 as pichat, which you will not meet in practice.",
  "exposure": {
    "verdict": "never",
    "note": "This is an internal cluster path that moves raw data parts between replicas; keep it on the cluster network and never route it from the internet."
  },
  "checkCommand": "sudo lsof -nP -iTCP:9009 -sTCP:LISTEN",
  "links": [
    {
      "title": "ClickHouse — network ports (9009 inter-server communication)",
      "url": "https://clickhouse.com/docs/guides/sre/network-ports",
      "kind": "official-docs"
    },
    {
      "title": "ClickHouse/ClickHouse on GitHub",
      "url": "https://github.com/ClickHouse/ClickHouse",
      "kind": "github"
    },
    {
      "title": "IANA Service Name and Transport Protocol Port Number Registry — 9009",
      "url": "https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=9009",
      "kind": "iana"
    }
  ],
  "ianaName": "pichat"
}