ADR 011: Monitoring
ADR 011: Monitoring
Changelog
08-06-2018: Initial draft 11-06-2018: Reorg after @xla comments 13-06-2018: Clarification about usage of labels
Context
In order to bring more visibility into Tendermint, we would like it to report metrics and, maybe later, traces of transactions and RPC queries. See https://github.com/tendermint/tendermint/issues/986.
A few solutions were considered:
- Prometheus a) Prometheus API b) go-kit metrics package as an interface plus Prometheus c) telegraf d) new service, which will listen to events emitted by pubsub and report metrics
- OpenCensus
1. Prometheus
Prometheus seems to be the most popular product out there for monitoring. It has a Go client library, powerful queries, alerts.
a) Prometheus API
We can commit to using Prometheus in Tendermint, but I think Tendermint users should be free to choose whatever monitoring tool they feel will better suit their needs (if they don't have existing one already). So we should try to abstract interface enough so people can switch between Prometheus and other similar tools.
b) go-kit metrics package as an interface
metrics package provides a set of uniform interfaces for service instrumentation and offers adapters to popular metrics packages:
https://godoc.org/github.com/go-kit/kit/metrics#pkg-subdirectories
Comparing to Prometheus API, we're losing customisability and control, but gaining freedom in choosing any instrument from the above list given we will extract metrics creation into a separate function (see "providers" in node/node.go).
c) telegraf
Unlike already discussed options, telegraf does not require modifying Tendermint source code. You create something called an input plugin, which polls Tendermint RPC every second and calculates the metrics itself.
While it may sound good, but some metrics we want to report are not exposed via RPC or pubsub, therefore can't be accessed externally.
d) service, listening to pubsub
Same issue as the above.
2. opencensus
opencensus provides both metrics and tracing, which may be important in the future. It's API looks different from go-kit and Prometheus, but looks like it covers everything we need.
Unfortunately, OpenCensus go client does not define any interfaces, so if we want to abstract away metrics we will need to write interfaces ourselves.
List of metrics
| Name | Type | Description | |
|---|---|---|---|
| A | consensus_height | Gauge | |
| A | consensus_validators | Gauge | Number of validators who signed |
| A | consensus_validators_power | Gauge | Total voting power of all validators |
| A | consensus_missing_validators | Gauge | Number of validators who did not sign |
| A | consensus_missing_validators_power | Gauge | Total voting power of the missing validators |
| A | consensus_byzantine_validators | Gauge | Number of validators who tried to double sign |
| A | consensus_byzantine_validators_power | Gauge | Total voting power of the byzantine validators |
| A | consensus_block_interval | Timing | Time between this and last block (Block.Header.Time) |
| consensus_block_time | Timing | Time to create a block (from creating a proposal to commit) | |
| consensus_time_between_blocks | Timing | Time between committing last block and (receiving proposal creating proposal) | |
| A | consensus_rounds | Gauge | Number of rounds |
| consensus_prevotes | Gauge | ||
| consensus_precommits | Gauge | ||
| consensus_prevotes_total_power | Gauge | ||
| consensus_precommits_total_power | Gauge | ||
| A | consensus_num_txs | Gauge | |
| A | mempool_size | Gauge | |
| A | consensus_total_txs | Gauge | |
| A | consensus_block_size | Gauge | In bytes |
| A | p2p_peers | Gauge | Number of peers node's connected to |
A - will be implemented in the fist place.
Proposed solution
Status
Implemented
Consequences
Positive
Better visibility, support of variety of monitoring backends
Negative
One more library to audit, messing metrics reporting code with business domain.