Telemetry

The Consul agent collects various runtime metrics about the performance of different libraries and subsystems. These metrics are aggregated on a ten second interval and are retained for one minute.

To view this data, you must send a signal to the Consul process: on Unix, this is USR1 while on Windows it is BREAK. Once Consul receives the signal, it will dump the current telemetry information to the agent’s stderr.

This telemetry information can be used for debugging or otherwise getting a better view of what Consul is doing. Review the Monitoring and Metrics tutorial to learn how collect and interpret Consul data.

Additionally, if the telemetry configuration options are provided, the telemetry information will be streamed to a statsite or statsd server where it can be aggregated and flushed to Graphite or any other metrics store. For a configuration example for Telegraf, review the Monitoring with Telegraf tutorial.

This information can also be viewed with the metrics endpoint in JSON format or using Prometheus format.

Below is sample output of a telemetry dump:

[2014-01-29 10:56:50 -0800 PST][G] 'consul-agent.runtime.num_goroutines': 19.000
[2014-01-29 10:56:50 -0800 PST][G] 'consul-agent.runtime.alloc_bytes': 755960.000
[2014-01-29 10:56:50 -0800 PST][G] 'consul-agent.runtime.malloc_count': 7550.000
[2014-01-29 10:56:50 -0800 PST][G] 'consul-agent.runtime.free_count': 4387.000
[2014-01-29 10:56:50 -0800 PST][G] 'consul-agent.runtime.heap_objects': 3163.000
[2014-01-29 10:56:50 -0800 PST][G] 'consul-agent.runtime.total_gc_pause_ns': 1151002.000
[2014-01-29 10:56:50 -0800 PST][G] 'consul-agent.runtime.total_gc_runs': 4.000
[2014-01-29 10:56:50 -0800 PST][C] 'consul-agent.agent.ipc.accept': Count: 5 Sum: 5.000
[2014-01-29 10:56:50 -0800 PST][C] 'consul-agent.agent.ipc.command': Count: 10 Sum: 10.000
[2014-01-29 10:56:50 -0800 PST][C] 'consul-agent.serf.events': Count: 5 Sum: 5.000
[2014-01-29 10:56:50 -0800 PST][C] 'consul-agent.serf.events.foo': Count: 4 Sum: 4.000
[2014-01-29 10:56:50 -0800 PST][C] 'consul-agent.serf.events.baz': Count: 1 Sum: 1.000
[2014-01-29 10:56:50 -0800 PST][S] 'consul-agent.memberlist.gossip': Count: 50 Min: 0.007 Mean: 0.020 Max: 0.041 Stddev: 0.007 Sum: 0.989
[2014-01-29 10:56:50 -0800 PST][S] 'consul-agent.serf.queue.Intent': Count: 10 Sum: 0.000
[2014-01-29 10:56:50 -0800 PST][S] 'consul-agent.serf.queue.Event': Count: 10 Min: 0.000 Mean: 2.500 Max: 5.000 Stddev: 2.121 Sum: 25.000

Key Metrics

These are some metrics emitted that can help you understand the health of your cluster at a glance. For a full list of metrics emitted by Consul, see Metrics Reference

Transaction timing

Why they’re important: Taken together, these metrics indicate how long it takes to complete write operations in various parts of the Consul cluster. Generally these should all be fairly consistent and no more than a few milliseconds. Sudden changes in any of the timing values could be due to unexpected load on the Consul servers, or due to problems on the servers themselves.

What to look for: Deviations (in any of these metrics) of more than 50% from baseline over the previous hour.

Leadership changes

Why they’re important: Normally, your Consul cluster should have a stable leader. If there are frequent elections or leadership changes, it would likely indicate network issues between the Consul servers, or that the Consul servers themselves are unable to keep up with the load.

What to look for: For a healthy cluster, you’re looking for a lastContact lower than 200ms, leader > 0 and candidate == 0. Deviations from this might indicate flapping leadership.

Autopilot

Why it’s important: Obviously, you want your cluster to be healthy.

What to look for: Alert if healthy is 0.

Memory usage

Why they’re important: Consul keeps all of its data in memory. If Consul consumes all available memory, it will crash.

What to look for: If consul.runtime.sys_bytes exceeds 90% of total available system memory.

Garbage collection

Why it’s important: GC pause is a “stop-the-world” event, meaning that all runtime threads are blocked until GC completes. Normally these pauses last only a few nanoseconds. But if memory usage is high, the Go runtime may GC so frequently that it starts to slow down Consul.

What to look for: Warning if total_gc_pause_ns exceeds 2 seconds/minute, critical if it exceeds 5 seconds/minute.

NOTE: total_gc_pause_ns is a cumulative counter, so in order to calculate rates (such as GC/minute), you will need to apply a function such as InfluxDB’s non_negative_difference().

Network activity - RPC Count

Why they’re important: These measurements indicate the current load created from a Consul agent, including when the load becomes high enough to be rate limited. A high RPC count, especially from consul.client.rpcexceeded meaning that the requests are being rate-limited, could imply a misconfigured Consul agent.

What to look for: Sudden large changes to the consul.client.rpc metrics (greater than 50% deviation from baseline). consul.client.rpc.exceeded or consul.client.rpc.failed count > 0, as it implies that an agent is being rate-limited or fails to make an RPC request to a Consul server

When telemetry is being streamed to an external metrics store, the interval is defined to be that store’s flush interval. Otherwise, the interval can be assumed to be 10 seconds when retrieving metrics from the built-in store using the above described signals.

Metrics Reference

This is a full list of metrics emitted by Consul.

Server Health

These metrics are used to monitor the health of the Consul servers.

Cluster Health

These metrics give insight into the health of the cluster as a whole.

Connect Built-in Proxy Metrics

Consul Connect’s built-in proxy is by default configured to log metrics to the same sink as the agent that starts it.

When running in this mode it emits some basic metrics. These will be expanded upon in the future.

All metrics are prefixed with consul.proxy.<proxied-service-id> to distinguish between multiple proxies on a given host. The table below use web as an example service name for brevity.

Labels

Most labels have a dst label and some have a src label. When using metrics sinks and timeseries stores that support labels or tags, these allow aggregating the connections by service name.

Assuming all services are using a managed built-in proxy, you can get a complete overview of both number of open connections and bytes sent and received between all services by aggregating over these metrics.

For example aggregating over all upstream (i.e. outbound) connections which have both src and dst labels, you can get a sum of all the bandwidth in and out of a given service or the total number of connections between two services.

Metrics Reference

The standard go runtime metrics are exported by go-metrics as with Consul agent. The table below describes the additional metrics exported by the proxy.