Monitoring rqlite

How to monitor rqlite

Status API

rqlite serves diagnostic and statistical information, as well as detailed information about the underlying Raft system, at /status. Assuming the rqlite node is started with default settings you can issue a curl command like so to retrieve this information:

curl localhost:4001/status?pretty

The use of the URL param pretty is optional, and results in pretty-printed JSON responses. The output of this endpoint could be periodically written to a monitoring system, allowing the performance of rqlite to be tracked over time.

You can also request the same status information via the rqlite shell:

$ ./rqlite 
Welcome to the rqlite CLI. Enter ".help" for usage hints.> .status
  build_time: unknown
  commit: unknown
  version: 5
  branch: unknown
  auth: disabled
  start_time: 2019-12-23T22:34:46.215507011-05:00
  uptime: 16.963009139s
  num_goroutine: 9
  version: go1.13

Nodes API

The nodes API returns basic information for nodes in the cluster, as seen by the node receiving the nodes request. The receiving node will also check whether it can actually connect to all other nodes in the cluster. This is an effective way to determine the cluster leader, and the leader’s HTTP API address. It can also be used to check if the cluster is basically running – if the other nodes are reachable, it probably is.

By default, the node only checks if voting nodes are contactable.

curl localhost:4001/nodes?pretty

# Request an improved JSON format, which is easier for parsing.
curl localhost:4001/nodes?pretty&ver=2

# Also check non-voting nodes.
curl localhost:4001/nodes?nonvoters&pretty

# Give up if all nodes don't respond within 5 seconds. Default is 30 seconds.
curl localhost:4001/nodes?timeout=5s

You can also request the same nodes information via the rqlite shell:

$ ./rqlite
Welcome to the rqlite CLI. Enter ".help" for usage hints.> .nodes
  api_addr: http://localhost:4001
  reachable: true
  leader: true
  api_addr: http://localhost:4003
  reachable: true
  leader: false
  api_addr: http://localhost:4005
  reachable: true
  leader: false

Readiness checks

rqlite nodes serve a “ready” status at /readyz. The endpoint will return HTTP 200 OK if the node is ready to respond to database requests and cluster management operations. An example access is shown below.

$ curl localhost:4001/readyz
[+]node ok
[+]leader ok
[+]store ok

If you wish to check if the node is running, and responding to HTTP requests, regardless of Leader status, add noleader to the URL. This form may be more useful for automated deployments, which simply need to know if the node is responsive.

$ curl localhost:4001/readyz?noleader
[+]node ok

Strictly speaking readyz indicates that the database is ready to respond to all write requests, and all read requests with Weak or Strong Read Consistency. A rqlite node can always respond to read requests with None consistency, assuming the local database is accessible. Of course, the results you get back from a None request may be quite a bit different than what the rest of the cluster considers committed.

sync flag

You can tell /readyz to block until the node has received the log entry equal to Leader’s Commit Index as it was set by the latest Heartbeat received from the Leader. This allows you to check that a node is “caught up” with the Leader. To enable this check add sync to the URL. For example:

$ curl localhost:4001/readyz?sync&timeout=5s
[+]node ok
[+]leader ok
[+]store ok
[+]sync ok

In the example above /readyz will block, for at most 5 seconds, until the receiving node is in sync with the Leader’s Commit Index. The timeout, if not explicitly set, is 30 seconds. If the node receiving such a request is itself the Leader, this flag has no effect as the Leader is always caught up with itself.

expvar support

rqlite also exports expvar information, which are mostly counters of various rqlite activity. The standard expvar information, as well as some custom information, is exposed. This data can be retrieved like so (assuming the node is started in its default configuration):

curl localhost:4001/debug/vars

You can optionally set the query parmameter key if you wish to retrieve just a subsection of the expvar output e.g. the URL localhost:4001/debug/vars?key=http will return just HTTP information.

You can also request the same expvar information via the CLI:

$ rqlite> .expvar
cmdline: [./rqlited data]
  execute_transactions: 0
  execution_errors: 1
  executions: 1
  queries: 0
  query_transactions: 0
  backups: 0
  executions: 0
  queries: 0
  Mallocs: 8950
  HeapSys: 2.588672e+06
  StackInuse: 557056
  LastGC: 0...

Similar to the status output, the output of this endpoint could be periodically written to a monitoring system, allowing the performance of rqlite to be tracked over time.

pprof support

pprof information is available by default and can be accessed as follows:

curl localhost:4001/debug/pprof/cmdline
curl localhost:4001/debug/pprof/profile
curl localhost:4001/debug/pprof/symbol
Last modified February 21, 2024: Update (5980947)