Skip to content

How to harden a Dragonfly container (and is dragonfly:latest safe for your cache?)

Dragonfly is a drop-in Redis and Memcached replacement: it holds session state, cache entries, queues, and often the working set of data your app reaches for on every request. A stock docker run dragonflydb/dragonfly:latest holds that data 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 shared network cache, an in-memory store that only its co-located application talks to over the loopback 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.

Graded from a read-only inspect of a running container started from docker.dragonflydb.io/dragonflydb/dragonfly:latest with plain docker run defaults, its entrypoint overridden with sleep purely to keep it alive. The scan itself executes nothing inside the container. It is the same data behind its isolation scorecard. How scoring works →

Where the default configuration leaks

ironctl scan grades seven independent containment boundaries. On a default docker run dragonflydb/dragonfly:latest, 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 Dragonfly process that escapes as root escapes as root on the host, next to the very data it was holding in memory and its snapshot files on disk. And a store that can reach arbitrary destinations is one that can quietly ship your cached data out the moment a protocol-parsing 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-dragonfly --fix prints one remediation per failed dimension, then one hardened run. For dragonflydb/dragonfly:latest:

  • --user 65532:65532 (Non-root user, +15): pin a non-root uid so an escape does not begin as host uid 0. Point the snapshot directory at a volume this uid owns.
  • --cap-drop=ALL (Dropped capabilities, +16): drop every Linux capability; Dragonfly needs none of the default set to serve its Redis-compatible protocol on a high port.
  • --read-only --tmpfs /tmp (Read-only rootfs, +10): make the root filesystem read-only and mount /data as an explicit writable volume for snapshots. 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 client is the app on the same host or pod and reaches Dragonfly over the loopback of a shared network namespace, cut the NIC entirely. Nothing external can connect, and the store cannot phone home.

When network=none is not honest

If Dragonfly is a shared cache that many services across the network connect to, or you run replication to replicas, you cannot use --network=none; it has to accept those connections. In that case put it on a user-defined network scoped to just its clients and replicas, 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 dragonfly docker.dragonflydb.io/dragonflydb/dragonfly:latest

# After: 100/100, grade A (co-located app on loopback, no network needed)
docker run -d --name dragonfly-hardened \
  --user 65532:65532 \
  --cap-drop=ALL \
  --security-opt=no-new-privileges \
  --read-only --tmpfs /tmp \
  -v dragonfly-data:/data \
  --network=none \
  docker.dragonflydb.io/dragonflydb/dragonfly:latest

Rescan: ironctl scan dragonfly-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 in-memory store does not need to talk to anything but the app on the other side of its loopback. Run it as a shared network cache instead and the honest ceiling is 89/100, grade B, called out above.

Verify it on your own Dragonfly

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

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

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

Keep going