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How to harden a QuestDB container (and is questdb:8.2.1 safe for your metrics?)

QuestDB ingests high-throughput time-series data: sensor readings, financial ticks, application metrics, the append-only history you query for trends. A stock docker run questdb/questdb:8.2.1 keeps that store behind a boundary weaker than the data deserves. Graded on IronClaw's seven-dimension containment scale, the default configuration scores 48 of 100, grade D (porous). Higher is safer. Unlike a broker or a proxy, a time-series database that only its co-located application writes to can close every dimension, including the network. A few runtime flags take the same image to a full 100 of 100, grade A. Here are the exact gaps and fixes from the scan data.

Every number here comes from a read-only docker inspect of questdb:8.2.1, the same data behind its isolation scorecard. No workload is executed. How scoring works →

Where the default configuration leaks

ironctl scan grades seven independent containment boundaries. On a default docker run questdb/questdb:8.2.1, three fail and one warns:

Dimension Verdict Score What the scan found
Non-root user (uid != 0) ❌ FAIL 0/15 runs as root (uid 0); a container escape starts with host-uid 0
Dropped capabilities ❌ FAIL 4/20 default capability set retained (CAP_NET_RAW, CAP_MKNOD, and more)
Seccomp profile ✅ PASS 15/15 seccomp profile active
Network isolation / egress ⚠️ WARN 4/15 network=bridge: outbound egress is possible
Read-only root filesystem ❌ FAIL 0/10 root filesystem is writable
No docker.sock exposure ✅ PASS 15/15 no control socket mounted
No shared host namespaces ✅ PASS 10/10 no host PID/IPC/network sharing

The two that should worry you most are root and egress. A QuestDB process that escapes as root escapes as root on the host, right next to the column files it was serving. And a database that can reach arbitrary destinations is one that can quietly exfiltrate your entire history the moment an ingestion-protocol or HTTP-API CVE lands code execution. The default capability set and writable rootfs widen and entrench that foothold.

Harden it: the exact --fix remediation

ironctl scan my-questdb --fix prints one remediation per failed dimension, then one hardened run. For questdb:8.2.1:

  • --user 10001:10001 (Non-root user, +15): pin a non-root uid so an escape does not begin as host uid 0. Point the data root at a volume this uid owns.
  • --cap-drop=ALL (Dropped capabilities, +16): drop every Linux capability; QuestDB needs none of the default set to serve its HTTP, PostgreSQL-wire, and InfluxDB-line ports.
  • --read-only --tmpfs /tmp (Read-only rootfs, +10): make the root filesystem read-only and mount /var/lib/questdb as an explicit writable volume. Removes the persistence surface.
  • --network=none (Network isolation, +11 to the full 15): this is the dimension a co-located store can actually max out. If the only writer is an application on the same host or pod reaching QuestDB over the loopback of a shared network namespace, cut the NIC entirely. Nothing external can connect, and the database cannot phone home.

When network=none is not honest

If a remote fleet pushes metrics over the network, or dashboard users hit the web console and query API, you cannot use --network=none; the store has to accept those connections. In that case put it on a user-defined network scoped to just its writers and clients, with no default route out. That holds the network dimension at a WARN (4 of 15) and the honest ceiling becomes 89 of 100, grade B, the same as a broker. Use --network=none only for the single-application, co-located case.

Before and after

# Before: 48/100, grade D
docker run -d --name questdb questdb/questdb:8.2.1

# After: 100/100, grade A (co-located store, no network needed)
docker run -d --name questdb-hardened \
  --user 10001:10001 \
  --cap-drop=ALL \
  --security-opt=no-new-privileges \
  --read-only --tmpfs /tmp \
  -v questdb-data:/var/lib/questdb \
  --network=none \
  questdb/questdb:8.2.1

Rescan: ironctl scan questdb-hardened reports 100/100 grade A. A 52-point swing with no custom image build, just the right flags. Every dimension is closed because a co-located time-series database does not need to talk to anything but the app on the other side of its loopback. That is the top grade, reserved for datastores whose clients live next to them.

Verify it on your own QuestDB

# install (Homebrew)
brew install ironsecco/ironclaw/ironclaw

# grade your running container, then print the fixes
ironctl scan my-questdb
ironctl scan my-questdb --fix

ironctl scan also reads a docker-compose.yml service or a Kubernetes manifest, so you can grade the QuestDB in your stack, not just a bare docker run.

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