Best Practices

Production deployment tips for running lplex on a boat.

CAN interface setup

Set up the SocketCAN interface at boot. The standard NMEA 2000 bitrate is 250 kbit/s.

# Bring up the interface
sudo ip link set can0 type can bitrate 250000
sudo ip link set can0 up

# Verify
ip -details link show can0

For persistent setup, create a systemd network file:

# /etc/systemd/network/80-can0.network
[Match]
Name=can0

[CAN]
BitRate=250000

Or use /etc/network/interfaces on Debian:

auto can0
iface can0 inet manual
    pre-up /sbin/ip link set can0 type can bitrate 250000
    up /sbin/ip link set can0 up
    down /sbin/ip link set can0 down

Ring buffer sizing

The default ring buffer holds 64k entries. At a typical bus rate of ~340 frames/sec, this gives roughly 3 minutes of history. If your buffered clients need more replay window, the buffer timeout should match what the journal can provide.

The ring buffer size is fixed at compile time (power of 2). For most boats, the default is fine.

Block size tuning

The default block size is 256 KB. Tradeoffs:

Size	Pros	Cons
Smaller (64 KB)	Less data lost on crash, faster seeking	More overhead, slightly worse compression
Larger (1 MB)	Better compression ratio, less overhead	More data at risk on crash

256 KB is a good balance. Only change this if you have a specific reason.

Compression

Use zstd (the default). It gives ~4x compression with negligible CPU overhead. The zstd-dict mode offers slightly better ratios by training per-block dictionaries but uses more CPU. none is only useful for debugging or if you need O(1) byte-offset seeking.

Journaling recommendations

• Always enable journaling on the boat. Disk is cheap, lost data is not.
• Set rotation to 1 hour (PT1H) for manageable file sizes.
• Enable retention with at least 30 days max-age.
• If replicating to cloud, set archival trigger to on-rotate so files are uploaded as soon as they're complete.

journal {
  dir = /var/log/lplex
  compression = zstd
  rotate.duration = PT1H

  retention {
    max-age = P30D
    max-size = 10737418240  # 10 GB
    soft-pct = 80
    overflow-policy = delete-unarchived
  }

  archive {
    command = /usr/local/bin/archive-to-s3
    trigger = on-rotate
  }
}

Monitoring bus silence

lplex alerts when no CAN frames are received for a configurable duration. This catches cable disconnects, interface failures, or power issues.

bus-silence-timeout = PT30S
health.bus-silence-threshold = PT30S

The health endpoint (GET /healthz) reports unhealthy when the bus has been silent longer than the threshold.

Systemd hardening

The .deb package includes a basic systemd unit. For production, consider adding:

[Service]
# Restrict capabilities
CapabilityBoundingSet=CAP_NET_RAW CAP_NET_ADMIN
AmbientCapabilities=CAP_NET_RAW CAP_NET_ADMIN

# Filesystem restrictions
ProtectSystem=strict
ReadWritePaths=/var/log/lplex
ProtectHome=yes

# Restart policy
Restart=always
RestartSec=5

# Resource limits
MemoryMax=256M

Multiple CAN interfaces

lplex currently supports a single CAN interface per process. If you have multiple buses, run multiple instances on different ports:

lplex -interface can0 -port 8089 -journal-dir /var/log/lplex/can0
lplex -interface can1 -port 8090 -journal-dir /var/log/lplex/can1