Synopsis
Gather relevant insights about your application and modules with custom metrics and telemetry.
telemetry package. To enable telemetrics, set telemetry.enabled = true in the app.toml config file.
The Cosmos SDK currently supports enabling in-memory and prometheus as telemetry sinks. In-memory sink is always attached (when the telemetry is enabled) with 10 second interval and 1 minute retention. This means that metrics will be aggregated over 10 seconds, and metrics will be kept alive for 1 minute.
To query active metrics (see retention note above) you have to enable API server (api.enabled = true in the app.toml). Single API endpoint is exposed: http://localhost:1317/metrics?format={text|prometheus}, the default being text.
Emitting metrics
If telemetry is enabled via configuration, a single global metrics collector is registered via the go-metrics library. This allows emitting and collecting metrics through simple API. Example:telemetry package directly, which provides wrappers around metric APIs
that include adding useful labels, or they must use the go-metrics library directly. It is preferable
to add as much context and adequate dimensionality to metrics as possible, so the telemetry package
is advised. Regardless of the package or method used, the Cosmos SDK supports the following metrics
types:
- gauges
- summaries
- counters
Labels
Certain components of modules will have their name automatically added as a label (e.g.BeginBlock).
Operators may also supply the application with a global set of labels that will be applied to all
metrics emitted using the telemetry package (e.g. chain-id). Global labels are supplied as a list
of [name, value] tuples.
Example:
Cardinality
Cardinality is key, specifically label and key cardinality. Cardinality is how many unique values of something there are. So there is naturally a tradeoff between granularity and how much stress is put on the telemetry sink in terms of indexing, scrape, and query performance. Developers should take care to support metrics with enough dimensionality and granularity to be useful, but not increase the cardinality beyond the sink’s limits. A general rule of thumb is to not exceed a cardinality of 10. Consider the following examples with enough granularity and adequate cardinality:- begin/end blocker time
- tx gas used
- block gas used
- amount of tokens minted
- amount of accounts created
- transfers between accounts with amount
- voting/deposit amount from unique addresses