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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. 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 ### 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: An SD mechanism has to implement the `Discoverer` Interface:
```go ```go
type Discoverer interface { 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. 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 `TargetGroup`s, or only changed and new `TargetGroup`s, down the channel. `Manager` will handle 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. both cases.
For example if we had a discovery mechanism and it retrieves the following groups: For example if we had a discovery mechanism and it retrieves the following groups:
``` ```
[]config.TargetGroup{ []targetgroup.Group{
{ {
Targets: []model.LabelSet{ 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{ Targets: []model.LabelSet{
{ {
"__instance__": "10.11.122.11:6001", "__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: 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, Targets: nil,
"Source": "file2", "Source": "file2",
} }