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doc: add monitoring section to admin doc

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Xiang Li 2015-09-04 13:48:00 -07:00
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Documentation/admin_guide.md
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@ -39,6 +39,74 @@ If `--wal-dir` flag is set, etcd will write the write ahead log files to the spe
If you are spinning up multiple clusters for testing it is recommended that you specify a unique initial-cluster-token for the different clusters.
This can protect you from cluster corruption in case of mis-configuration because two members started with different cluster tokens will refuse members from each other.
#### Monitoring
It is important to monitor your production etcd cluster for healthy information and runtime metrics.
##### Health Monitoring
At lowest level, etcd exposes health information via HTTP at `/health` in JSON format. If it returns `{"health": "true"}`, then the cluster is healthy. Please note the `/health` endpoint is still an experimental one as in etcd 2.2.
```
$ curl -L http://127.0.0.1:2379/health
{"health": "true"}
```
You can also use etcdctl to check the cluster-wide health information. It will contact all the members of the cluster and collect the health information for you.
```
$./etcdctl cluster-health
member 8211f1d0f64f3269 is healthy: got healthy result from http://127.0.0.1:12379
member 91bc3c398fb3c146 is healthy: got healthy result from http://127.0.0.1:22379
member fd422379fda50e48 is healthy: got healthy result from http://127.0.0.1:32379
cluster is healthy
```
##### Runtime Metrics
etcd uses [Prometheus](http://prometheus.io/) for metrics reporting in the server. You can read more through the runtime metrics [doc](metrics.md).
#### Debugging
Debugging a distributed system can be difficult. etcd provides several ways to make debug
easier.
##### Enabling Debug Logging
When you want to debug etcd without stopping it, you can enable debug logging at runtime.
etcd exposes logging configuration at `/config/local/log`.
```
$ curl http://127.0.0.1:2379/config/local/log -XPUT -d '{"Level":"DEBUG"}'
$ # debug logging enabled
$
$ curl http://127.0.0.1:2379/config/local/log -XPUT -d '{"Level":"INFO"}'
$ # debug logging disabled
```
##### Debugging Variables
Debug variables are exposed for real-time debugging purposes. Developers who are familiar with etcd can utilize these variables to debug unexpected behavior. etcd exposes debug variables via HTTP at `/debug/vars` in JSON format. The debug variables contains
`cmdline`, `file_descriptor_limit`, `memstats` and `raft.status`.
`cmdline` is the command line arguments passed into etcd.
`file_descriptor_limit` is the max number of file descriptors etcd can utilize.
`memstats` is well explained [here](http://golang.org/pkg/runtime/#MemStats).
`raft.status` is useful when you want to debug low level raft issues if you are familiar with raft internals. In most cases, you do not need to check `raft.status`.
```json
{
"cmdline": ["./etcd"],
"file_descriptor_limit": 0,
"memstats": {"Alloc":4105744,"TotalAlloc":42337320,"Sys":12560632,"...":"..."},
"raft.status": {"id":"ce2a822cea30bfca","term":5,"vote":"ce2a822cea30bfca","commit":23509,"lead":"ce2a822cea30bfca","raftState":"StateLeader","progress":{"ce2a822cea30bfca":{"match":23509,"next":23510,"state":"ProgressStateProbe"}}}
}
```
#### Optimal Cluster Size
The recommended etcd cluster size is 3, 5 or 7, which is decided by the fault tolerance requirement. A 7-member cluster can provide enough fault tolerance in most cases. While larger cluster provides better fault tolerance the write performance reduces since data needs to be replicated to more machines.