Deployment

Data Persistence

Nexo stores all data under ./data/ by default:

data/
├── queues/     ← Queue messages (SQLite WAL)
├── streams/    ← Stream segments (append-only files)
└── pubsub/     ← Pub/Sub retained messages (JSON files)

In Docker, this directory lives inside the container — meaning data is lost when the container is removed. To persist data across restarts, mount a Docker volume:

# Simple: single volume for all brokers
docker run -d \
  -p 7654:7654 \
  -v nexo-data:/app/data \
  emanuelepifani/nexo

# Or bind to a host directory
docker run -d \
  -p 7654:7654 \
  -v /mnt/ssd/nexo:/app/data \
  emanuelepifani/nexo

Separate Disks (Advanced)

If your brokers have different I/O profiles (e.g. Streams write heavily, Queues need low latency), you can map each to a different disk using environment variables:

docker run -d \
  -p 7654:7654 \
  -e QUEUE_ROOT_PERSISTENCE_PATH=/data/queues \
  -e STREAM_ROOT_PERSISTENCE_PATH=/data/streams \
  -e PUBSUB_ROOT_PERSISTENCE_PATH=/data/pubsub \
  -v /mnt/fast-ssd:/data/queues \
  -v /mnt/large-hdd:/data/streams \
  -v /mnt/fast-ssd:/data/pubsub \
  emanuelepifani/nexo

For most deployments, a single volume is sufficient.

Max Payload Size

Nexo enforces a maximum payload size per frame to prevent memory exhaustion from oversized or malicious requests. Any frame exceeding this limit is rejected at the protocol level before allocating memory.

The default limit is 10 MB. To increase it (e.g. for large stream messages or queue payloads):

docker run -p 7654:7654 -e MAX_PAYLOAD_SIZE=52428800 emanuelepifani/nexo  # 50MB

Environment Variables

Variable	Default	Description
SERVER_HOST	127.0.0.1	Bind address (set to 0.0.0.0 to expose on all interfaces, e.g. in Docker)
SERVER_SOCKET_TCP_PORT	7654	Client TCP socket port
NEXO_LOG	error	Log level (error, warn, info, debug, trace)
MAX_PAYLOAD_SIZE	10485760	Max frame payload in bytes (10 MB)
QUEUE_ROOT_PERSISTENCE_PATH	./data/queues	Queue data directory
STREAM_ROOT_PERSISTENCE_PATH	./data/streams	Stream data directory
STREAM_STORAGE_QUEUE_CAPACITY	16384	Pending storage commands before publish backpressure
PUBSUB_ROOT_PERSISTENCE_PATH	./data/pubsub	Pub/Sub data directory