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All configuration is via environment variables.
VariableDefaultDescription
MERIDIAN_BIND0.0.0.0:3000TCP bind address
MERIDIAN_DATA_DIR./dataPath to sled storage directory
MERIDIAN_SIGNING_KEY(random)64-char hex ed25519 seed (32 bytes)
MERIDIAN_WEBHOOK_URL(unset)HTTP endpoint to receive webhook events
MERIDIAN_WEBHOOK_SECRET(unset)Secret for X-Meridian-Signature HMAC-SHA256

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MERIDIAN_SIGNING_KEY

Generate a secure key: 
openssl rand -hex 32
This key is used to sign and verify auth tokens. Keep it secret and back it up — losing it invalidates all issued tokens. If unset, a random key is generated at startup. This is fine for local development but not for production (tokens become invalid on restart).

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Webhooks

When MERIDIAN_WEBHOOK_URL is set, Meridian sends a POST request to that URL after every successful CRDT operation. Payload 
{
  "ns": "my-room",
  "crdt_id": "counter",
  "source": "http",
  "timestamp_ms": 1712345678901
}
source is either "http" (REST op) or "ws" (WebSocket op). Signature verification Every request includes an X-Meridian-Signature header containing HMAC-SHA256(secret, body) as a lowercase hex string. 
import { createHmac } from "crypto";

const signature = createHmac("sha256", process.env.MERIDIAN_WEBHOOK_SECRET!)
  .update(rawBody)
  .digest("hex");

if (signature !== req.headers["x-meridian-signature"]) {
  return res.status(401).end();
}
Failed deliveries are retried up to 3 times with exponential backoff (200ms, 400ms, 800ms). Events are dropped if the internal queue (1024 slots) is full.

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Rate limiting

Each token is limited to 100 requests per second (sliding window). Requests over the limit return 429 Too Many Requests: 
{ "error": "rate_limited", "message": "too many requests" }

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Metrics

Meridian exposes a Prometheus-compatible metrics endpoint at GET /metrics (no authentication required).
MetricTypeDescription
meridian_ops_totalCounterCRDT operations applied, labeled by ns, crdt_id, op_type
meridian_ws_connections_activeGaugeActive WebSocket connections
meridian_wal_entries_totalCounterWAL entries written
Example Prometheus scrape config: 
scrape_configs:
  - job_name: meridian
    static_configs:
      - targets: ["localhost:3000"]
    metrics_path: /metrics

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MERIDIAN_DATA_DIR

Meridian uses sled as its embedded database. The data directory contains the sled tree files. In Docker, this is mounted as a named volume: 
volumes:
  - meridian-data:/data