Distributed Pixel Cache

Security & Setup

To establish communication between client and server nodes, first configure a shared secret in your policy.xml security policy configuration file:

<policy domain="cache" name="shared-secret" value="passphrase" stealth="true"/>

When the distributed pixel cache transmits image pixels, it secures the data through two primary mechanisms. First, it scrambles the pixel data, rendering it as random digital noise to anyone attempting to intercept or spy on the network. Second, it applies a tamper-proof cryptographic signature, ensuring the data originated from a trusted source and has not been altered or forged in transit. However, these built-in protection mechanisms are not cryptographically strong, meaning they remain vulnerable to sophisticated attacks and should not be relied upon for high-security environments. For truly secure communication across networks, you may need to implement dedicated cryptographic security measures such as encrypted tunnels or secure loopback configurations:

• Restrict to Loopback: If distributed caching is only used across processes on the same machine, bind the server strictly to 127.0.0.1 to eliminate adjacent network visibility.
• Enforce Encrypted Tunnels: For multi-host deployments, never expose the plaintext TCP port directly. Route traffic through an encrypted, authenticated tunnel (such as WireGuard, IPsec, or an SSH port forward) to provide confidentiality and integrity at the network layer.

Usage Examples

Single Remote / Localhost Cache

Start a single distributed pixel cache server and process an image utilizing defined resource limits:

$ magick -distribute-cache 6668 &  # start on localhost
$ magick -limit memory 1GiB -limit map 2GiB -limit disk 4GiB \
  -define registry:cache:hosts=localhost:6668 \
  myhugeimage.jpg -sharpen 5x2 myhugeimage.png

Restrict to Loopback (127.0.0.1) Example

Bind the server strictly to 127.0.0.1 to eliminate adjacent network visibility when processes run on the same machine:

$ magick -distribute-cache 127.0.0.1:6668 &  # bind strictly to loopback
$ magick -limit memory 1GiB -limit map 2GiB -limit disk 4GiB \
  -define registry:cache:hosts=127.0.0.1:6668 \
  myhugeimage.jpg -sharpen 5x2 myhugeimage.png

Multi-Server Cluster Cache

Deploy pixel cache servers on multiple hosts to distribute storage load:

$ magick -distribute-cache 6668 &  # start on 192.168.100.50
$ magick -distribute-cache 6668 &  # start on 192.168.100.51
$ magick -limit memory 1GiB -limit map 2GiB -limit disk 4GiB \
  -define registry:cache:hosts=192.168.100.50:6668,192.168.100.51:6668 \
  myhugeimage.jpg -sharpen 5x2 myhugeimage.png

When multiple hosts are listed, ImageMagick contacts servers in a round-robin fashion to distribute load across the cluster. Smaller images or operations below local -limit thresholds are allocated directly on the host desktop.

Performance & Compatibility Considerations