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Add retain flag to mqtt output to let brokers/servers cache measurements #4892

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Feb 12, 2019
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Add retain flag to mqtt output to let brokers/servers cache measurements #4892

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d1232df
Add "Retain" flag to MQTT output
p-kraszewski Oct 20, 2018
6c01529
Update README.md
p-kraszewski Oct 20, 2018
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7 changes: 6 additions & 1 deletion plugins/outputs/mqtt/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -32,10 +32,14 @@ This plugin writes to a [MQTT Broker](http://http://mqtt.org/) acting as a mqtt
# tls_key = "/etc/telegraf/key.pem"
## Use TLS but skip chain & host verification
# insecure_skip_verify = false

## When true, metrics will be sent in one MQTT message per flush. Otherwise,
## metrics are written one metric per MQTT message.
# batch = false

## When true, metric will have RETAIN flag set, making broker cache entries until someone
## actually reads it
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# retain = flase
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## Data format to output.
# data_format = "influx"
Expand All @@ -56,4 +60,5 @@ This plugin writes to a [MQTT Broker](http://http://mqtt.org/) acting as a mqtt
* `tls_cert`: TLS CERT
* `tls_key`: TLS key
* `insecure_skip_verify`: Use TLS but skip chain & host verification (default: false)
* `retain`: Set `retain` flag when publishing, instructing server to cache metric until someone reads it (default: false)
* `data_format`: [About Telegraf data formats](https://github.com/influxdata/telegraf/blob/master/docs/DATA_FORMATS_OUTPUT.md)
7 changes: 6 additions & 1 deletion plugins/outputs/mqtt/mqtt.go
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Expand Up @@ -49,6 +49,10 @@ var sampleConfig = `
## When true, metrics will be sent in one MQTT message per flush. Otherwise,
## metrics are written one metric per MQTT message.
# batch = false
## When true, metric will have RETAIN flag set, making broker cache entries until someone
## actually reads it
# retain = flase
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## Data format to output.
## Each data format has its own unique set of configuration options, read
Expand All @@ -68,6 +72,7 @@ type MQTT struct {
ClientID string `toml:"client_id"`
tls.ClientConfig
BatchMessage bool `toml:"batch"`
Retain bool

client paho.Client
opts *paho.ClientOptions
Expand Down Expand Up @@ -174,7 +179,7 @@ func (m *MQTT) Write(metrics []telegraf.Metric) error {
}

func (m *MQTT) publish(topic string, body []byte) error {
token := m.client.Publish(topic, byte(m.QoS), false, body)
token := m.client.Publish(topic, byte(m.QoS), m.Retain, body)
token.WaitTimeout(m.Timeout.Duration)
if token.Error() != nil {
return token.Error()
Expand Down