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1.7.1
1.7.1
  • Welcome
  • Getting Started
  • Downloads
  • VerneMQ / MQTT Introduction
  • Installing VerneMQ
    • Installing on Debian and Ubuntu
    • Installing on CentOS and RHEL
    • Running VerneMQ using Docker
  • Configuring VerneMQ
    • Introduction
    • Auth using files
    • Auth using a database
    • MQTT Options
    • MQTT Listeners
    • HTTP Listeners
    • Non-standard MQTT options
    • Websockets
    • Logging
    • Consumer session balancing
    • Plugins
    • Shared subscriptions
    • Advanced Options
    • Storage
    • MQTT Bridge
  • VerneMQ Clustering
    • Introduction
    • Inter-node Communication
    • Dealing with Netsplits
  • Live Administration
    • Introduction
    • Inspecting and managing sessions
    • Retained messages
    • Live reconfiguration
    • Managing Listeners
    • HTTP API
    • Tracing
  • Monitoring
    • Introduction
    • $SYSTree
    • Graphite
    • Prometheus
    • Health Checker
    • Status Page
  • Plugin Development
    • Introduction
    • Session lifecycle
    • Subscribe Flow
    • Publish Flow
    • Enhanced Auth Flow
    • Erlang Boilerplate
    • Lua Scripting Support
    • Webhooks
  • Misc
    • Loadtesting VerneMQ
    • Not a tuning guide
    • Change Open File Limits
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  • Examples

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  1. Configuring VerneMQ

Shared subscriptions

Working with shared subscriptions

A shared subscription is a mechanism for distributing messages to a set of subscribers to shared subscription topic, such that each message is received by only one subscriber. This contrasts with normal subscriptions where each subscriber will receive a copy of the published message.

A shared subscription is on the form $share/sharename/topic and subscribers to this topic will receive messages published to the topic topic. The messages will be distributed according to the defined distribution policy.

When subscribing to a shared subscription using command line tools remember to quote the topic as some command line shells, like bash, will otherwise expand the $share part of the topic as an environment variable.

Configuration

Currently three message distribution policies for shared subscriptions are supported: prefer_local, random and local_only. Under the random policy messages will be published to a random member of the shared subscription, if any exist. Under the prefer_local policy messages will be delivered to a random node-local member of the shared subscription, if none exist, the message will be delivered to a random member of the shared subscription on a remote cluster node. Under the local_only policy message will be delivered to a random node-local member of the shared subscription.

shared_subscription_policy = prefer_local

When a messages is being delivered to subscribers of a shared subscription, the message will be delivered to an online subscriber if possible, otherwise the message will be delivered to an offline subscriber.

Examples

Subscriptions Note: When subscribing to a shared topic, make sure to escape the $

So, for dash or bash shells

mosquitto_sub -h mqtt.example.io -p 1883 -q 2 -t \$share/group/topicname
mosquitto_sub -h mqtt.example.io -p 1883 -q 2 -t \$share/group/topicname/#

Publishing Note: When publishing to a shared topic, do not include the prefix $share/group/ as part of the publish topic name

mosquito_pub -h mqtt.example.io -p 1883 -t topicname -m "This is a test message"
mosquito_pub -h mqtt.example.io -p 1883 -t topicname/group1 -m "This is a test message"
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Last updated 5 years ago

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