[[cat-health]]
== cat health

`health` is a terse, one-line representation of the same information
from `/_cluster/health`.

[source,js]
--------------------------------------------------
GET /_cat/health?v
--------------------------------------------------
// CONSOLE
// TEST[s/^/PUT twitter\n{"settings":{"number_of_replicas": 0}}\n/]

[source,txt]
--------------------------------------------------
epoch      timestamp cluster       status node.total node.data shards pri relo init unassign pending_tasks max_task_wait_time active_shards_percent
1475871424 16:17:04  elasticsearch green           1         1      1   1    0    0        0             0                  -                100.0%
--------------------------------------------------
// TESTRESPONSE[s/1475871424 16:17:04/\\d+ \\d+:\\d+:\\d+/]
// TESTRESPONSE[s/elasticsearch/[^ ]+/ s/0                  -/\\d+ (-|\\d+(\\.\\d+)?[ms]+)/ _cat]

It has one option `ts` to disable the timestamping:

[source,js]
--------------------------------------------------
GET /_cat/health?v&ts=false
--------------------------------------------------
// CONSOLE
// TEST[s/^/PUT twitter\n{"settings":{"number_of_replicas": 0}}\n/]

which looks like:

[source,txt]
--------------------------------------------------
cluster       status node.total node.data shards pri relo init unassign pending_tasks max_task_wait_time active_shards_percent
elasticsearch green           1         1      1   1    0    0        0             0                  -                100.0%
--------------------------------------------------
// TESTRESPONSE[s/elasticsearch/[^ ]+/ s/0                  -/\\d+ (-|\\d+(\\.\\d+)?[ms]+)/ _cat]

A common use of this command is to verify the health is consistent
across nodes:

[source,sh]
--------------------------------------------------
% pssh -i -h list.of.cluster.hosts curl -s localhost:9200/_cat/health
[1] 20:20:52 [SUCCESS] es3.vm
1384309218 18:20:18 foo green 3 3 3 3 0 0 0 0
[2] 20:20:52 [SUCCESS] es1.vm
1384309218 18:20:18 foo green 3 3 3 3 0 0 0 0
[3] 20:20:52 [SUCCESS] es2.vm
1384309218 18:20:18 foo green 3 3 3 3 0 0 0 0
--------------------------------------------------
// NOTCONSOLE

A less obvious use is to track recovery of a large cluster over
time. With enough shards, starting a cluster, or even recovering after
losing a node, can take time (depending on your network & disk). A way
to track its progress is by using this command in a delayed loop:

[source,sh]
--------------------------------------------------
% while true; do curl localhost:9200/_cat/health; sleep 120; done
1384309446 18:24:06 foo red 3 3 20 20 0 0 1812 0
1384309566 18:26:06 foo yellow 3 3 950 916 0 12 870 0
1384309686 18:28:06 foo yellow 3 3 1328 916 0 12 492 0
1384309806 18:30:06 foo green 3 3 1832 916 4 0 0
^C
--------------------------------------------------
// NOTCONSOLE

In this scenario, we can tell that recovery took roughly four minutes.
If this were going on for hours, we would be able to watch the
`UNASSIGNED` shards drop precipitously.  If that number remained
static, we would have an idea that there is a problem.

[float]
[[timestamp]]
=== Why the timestamp?

You typically are using the `health` command when a cluster is
malfunctioning.  During this period, it's extremely important to
correlate activities across log files, alerting systems, etc.

There are two outputs.  The `HH:MM:SS` output is simply for quick
human consumption.  The epoch time retains more information, including
date, and is machine sortable if your recovery spans days.