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docs: minor improvements to the service discovery README.md (#5296)

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i) Increased the size of the Service Discovery Readme title
ii) Changed `TargetGroups` to "target groups" as it has been relocated and renamed to another package.

Signed-off-by: tariqibrahim <tariq181290@gmail.com>
This commit is contained in:
Tariq Ibrahim 2019-03-03 10:48:03 -08:00 committed by Julius Volz
parent ab8e9b7423
commit 197e5ac597
1 changed files with 10 additions and 10 deletions
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20
discovery/README.md
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@ -1,4 +1,4 @@
### Service Discovery
# Service Discovery
This directory contains the service discovery (SD) component of Prometheus.
@ -131,23 +131,23 @@ the Prometheus server will be able to see them.
### The SD interface
A Service Discovery (SD) mechanism has to discover targets and provide them to Prometheus. We expect similar targets to be grouped together, in the form of a [`TargetGroup`](https://godoc.org/github.com/prometheus/prometheus/config#TargetGroup). The SD mechanism sends the targets down to prometheus as list of `TargetGroups`.
A Service Discovery (SD) mechanism has to discover targets and provide them to Prometheus. We expect similar targets to be grouped together, in the form of a [target group](https://godoc.org/github.com/prometheus/prometheus/discovery/targetgroup#Group). The SD mechanism sends the targets down to prometheus as list of target groups.
An SD mechanism has to implement the `Discoverer` Interface:
```go
type Discoverer interface {
Run(ctx context.Context, up chan<- []*config.TargetGroup)
Run(ctx context.Context, up chan<- []*targetgroup.Group)
}
```
Prometheus will call the `Run()` method on a provider to initialize the discovery mechanism. The mechanism will then send *all* the `TargetGroup`s into the channel.
Now the mechanism will watch for changes. For each update it can send all `TargetGroup`s, or only changed and new `TargetGroup`s, down the channel. `Manager` will handle
Prometheus will call the `Run()` method on a provider to initialize the discovery mechanism. The mechanism will then send *all* the target groups into the channel.
Now the mechanism will watch for changes. For each update it can send all target groups, or only changed and new target groups, down the channel. `Manager` will handle
both cases.
For example if we had a discovery mechanism and it retrieves the following groups:
```
[]config.TargetGroup{
[]targetgroup.Group{
{
Targets: []model.LabelSet{
{
@ -187,11 +187,11 @@ For example if we had a discovery mechanism and it retrieves the following group
}
```
Here there are two `TargetGroups` one group with source `file1` and another with `file2`. The grouping is implementation specific and could even be one target per group. But, one has to make sure every target group sent by an SD instance should have a `Source` which is unique across all the `TargetGroup`s of that SD instance.
Here there are two target groups one group with source `file1` and another with `file2`. The grouping is implementation specific and could even be one target per group. But, one has to make sure every target group sent by an SD instance should have a `Source` which is unique across all the target groups of that SD instance.
In this case, both the `TargetGroup`s are sent down the channel the first time `Run()` is called. Now, for an update, we need to send the whole _changed_ `TargetGroup` down the channel. i.e, if the target with `hostname: demo-postgres-2` goes away, we send:
In this case, both the target groups are sent down the channel the first time `Run()` is called. Now, for an update, we need to send the whole _changed_ target group down the channel. i.e, if the target with `hostname: demo-postgres-2` goes away, we send:
```
&config.TargetGroup{
&targetgroup.Group{
Targets: []model.LabelSet{
{
"__instance__": "10.11.122.11:6001",
@ -209,7 +209,7 @@ down the channel.
If all the targets in a group go away, we need to send the target groups with empty `Targets` down the channel. i.e, if all targets with `job: postgres` go away, we send:
```
&config.TargetGroup{
&targetgroup.Group{
Targets: nil,
"Source": "file2",
}