health is a terse, one-line representation of the same information
from /_cluster/health.
GET /_cat/health?v
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%
It has one option ts to disable the timestamping:
GET /_cat/health?v&ts=false
which looks like:
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%
A common use of this command is to verify the health is consistent across nodes:
% 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
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:
% 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
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.
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.