The local queue

Status pushes are written to a local SQLite file before the agent attempts to deliver them to the cloud. The file is the agent's durability layer. Pushes survive container restarts, daemon restarts, and the cloud being temporarily unreachable.

Behaviour

• Every status push enqueues a row in the local SQLite file (BUFFER_PATH, default ./observer-agent-buffer.db).
• A background drain controller pulls batches from the queue and posts them to the cloud's /api/agent/receiver/batch endpoint, up to 100 samples per request (agent 1.5.0 and later). A backlog of 10,000 rows drains in about 100 requests instead of 10,000.
• Successful posts ack and remove rows from the queue. When the cloud rejects individual rows in a batch (for example a sample with an out-of-range timestamp), those rows are dropped and logged; the rest of the batch is accepted normally.
• Failed posts back off exponentially. The queue continues to accept new pushes during the outage.
• When the queue reaches BUFFER_MAX_ROWS (default 10000), oldest entries are evicted to admit new ones.

The cloud is the source of truth for historical data. The local queue is a write-ahead log that protects against transient cloud failures, not a long-term store.

What the operator sees

The agent dashboard's queue panel shows three live numbers:

• depth: rows currently waiting.
• oldest_age_seconds: age of the oldest pending row.
• drain_backoff_ms: current backoff between drain attempts.

A growing depth combined with a non-zero backoff is the signature of cloud unreachability. Once the cloud is reachable again, the queue drains and depth returns to near zero.

Queue-driven alerts

The agent reports the queue numbers on every heartbeat. A sustained high queue (depth above 1000, or an oldest pending push older than 300 seconds) raises an agent.lag_high alert that surfaces on the agent detail page and as a webhook event when subscribed. Once the queue drains, the alert clears.