AMQP Connections
A connection is a TCP link between a client and LavinMQ. Both AMQP and MQTT clients establish connections.
AMQP Connections
AMQP connections follow the standard 0-9-1 lifecycle. See AMQP for protocol details.
MQTT Connections
MQTT connections follow the MQTT 3.1.x CONNECT/CONNACK handshake. See MQTT for protocol details.
Heartbeats
AMQP connections use heartbeats to detect dead peers. The heartbeat interval is negotiated during connection setup.
| Config Key | Section | Default | Description |
|---|---|---|---|
heartbeat |
[amqp] |
300 |
Heartbeat interval in seconds. Set to 0 to disable (not recommended). |
During connection setup, the client and server each propose a heartbeat interval and the lower of the two non-zero values wins. The server then expects to see traffic from the client at least that often; if nothing arrives within that interval plus a 5-second grace period, the connection is closed as dead. Setting the interval to 0 disables heartbeats entirely, which means dead peers are never detected and is not recommended.
Proxy Protocol
LavinMQ supports HAProxy PROXY protocol for preserving client IP addresses behind load balancers.
| Config Key | Section | Default | Description |
|---|---|---|---|
tcp_proxy_protocol |
[amqp] |
false |
Enable PROXY protocol on TCP, applies to AMQP and MQTT. Accepts true/false/yes/no; legacy 1/2 are treated as enabled, 0 disables. |
proxy_protocol_trusted_sources |
[amqp] |
(empty) | Comma-separated list of IPs and CIDR blocks (IPv4/IPv6) allowed to send PROXY headers, e.g. 10.0.0.1, 192.168.0.0/24, 2001:db8::/32. |
PROXY protocol v1 (text) and v2 (binary) are auto-detected. Only connections from trusted sources may send PROXY headers; headers from untrusted sources are ignored and the real connection address is used. If tcp_proxy_protocol is enabled but proxy_protocol_trusted_sources is empty, headers are accepted from all sources and a warning is logged at startup.
The address in a PROXY header is used for logging and for the connection listing. It never counts as loopback for the default_user_only_loopback check, not even from a listed source or a cluster follower. The address describes the client as seen by the proxy, not a connection on the broker host. A PROXY UNKNOWN header is rejected and the connection is closed, because the client address is not known. This also applies to an untrusted source, because the header is parsed before the source is checked.
Low Disk Space
When free disk space drops below 3 * segment_size or below free_disk_min, basic.publish returns a precondition_failed channel error until resources recover.
| Config Key | Section | Default | Description |
|---|---|---|---|
free_disk_min |
[main] |
0 |
Minimum free disk space in bytes. Publishing is blocked when free space drops below this value. |
free_disk_warn |
[main] |
0 |
Warning threshold in bytes. Emits warnings when free space drops below this value. |
segment_size |
[main] |
8388608 |
Segment file size (bytes). Publishing is also blocked when free space drops below 3 * segment_size. |
Connection Limits
Concurrent connections to a vhost can be capped with the max-connections vhost limit. The cap counts AMQP and MQTT connections together. Existing connections are unaffected once the cap is reached, or if the limit is later lowered below the current count.
| Limit | Default | Description |
|---|---|---|
max-connections |
(none) | Maximum concurrent connections per vhost. A negative value removes the cap. |
How a refused connection is reported depends on the protocol:
| Protocol | Refusal |
|---|---|
| AMQP | connection.close with reply code 530 (NOT_ALLOWED) |
| MQTT | CONNACK with return code 3 (server unavailable), then the socket is closed |
An MQTT client reconnecting with a client ID that already has an active connection is not refused at the cap, because session takeover closes the existing connection instead of adding one.
Set via the management API (PUT /api/vhost-limits/:vhost/max-connections) or lavinmqctl set_vhost_limits. See Vhosts.
TCP Tuning
| Config Key | Section | Default | Description |
|---|---|---|---|
tcp_nodelay |
[main] |
false |
Disable Nagle’s algorithm |
tcp_keepalive |
[main] |
60:10:3 |
Idle, interval, probes (colon-separated) |
tcp_recv_buffer_size |
[main] |
(system) | TCP receive buffer |
tcp_send_buffer_size |
[main] |
(system) | TCP send buffer |
socket_buffer_size |
[main] |
16384 |
Application socket buffer (bytes) |
Unix Domain Sockets
LavinMQ can listen on Unix domain sockets for all protocols:
| Config Key | Section | Description |
|---|---|---|
unix_path |
[amqp] |
AMQP Unix socket path |
unix_path |
[mqtt] |
MQTT Unix socket path |
unix_path |
[mgmt] |
HTTP Unix socket path |
Unix sockets auto-detect PROXY protocol headers if present to receive connection metadata.
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Help and feedback
We welcome your feedback and are eager to address any questions you may have about this piece or using LavinMQ. Join our Slack channel to connect with us directly. You can also find LavinMQ on GitHub.