Merge branch 'jl-add-custom-metrics-docs' into 'master'

Improvements for prometheus metrics documentation

See merge request gitlab-org/gitlab-ce!17838

doc/user/project/integrations/prometheus.md

@@ -2,7 +2,7 @@
 > [Introduced][ce-8935] in GitLab 9.0.
-GitLab offers powerful integration with [Prometheus] for monitoring key metrics your apps, directly within GitLab.
+GitLab offers powerful integration with [Prometheus] for monitoring key metrics of your apps, directly within GitLab.
 Metrics for each environment are retrieved from Prometheus, and then displayed
 within the GitLab interface.
@@ -12,17 +12,21 @@ There are two ways to setup Prometheus integration, depending on where your apps
 * For deployments on Kubernetes, GitLab can automatically [deploy and manage Prometheus](#managed-prometheus-on-kubernetes)
 * For other deployment targets, simply [specify the Prometheus server](#manual-configuration-of-prometheus).
-## Managed Prometheus on Kubernetes
+Once enabled, GitLab will automatically detect metrics from known services in the [metric library](#monitoring-ci-cd-environments).
+
+## Enabling Prometheus Integration
+
+### Managed Prometheus on Kubernetes
 > **Note**: [Introduced](https://gitlab.com/gitlab-org/gitlab-ce/issues/28916) in GitLab 10.5
 GitLab can seamlessly deploy and manage Prometheus on a [connected Kubernetes cluster](../clusters/index.md), making monitoring of your apps easy.
-### Requirements
+#### Requirements
 * A [connected Kubernetes cluster](../clusters/index.md)
 * Helm Tiller [installed by GitLab](../clusters/index.md#installing-applications)
-### Getting started
+#### Getting started
 Once you have a connected Kubernetes cluster with Helm installed, deploying a managed Prometheus is as easy as a single click.
@@ -32,7 +36,7 @@ Once you have a connected Kubernetes cluster with Helm installed, deploying a ma
 ![Managed Prometheus Deploy](img/prometheus_deploy.png)
-### About managed Prometheus deployments
+#### About managed Prometheus deployments
 Prometheus is deployed into the `gitlab-managed-apps` namespace, using the [official Helm chart](https://github.com/kubernetes/charts/tree/master/stable/prometheus). Prometheus is only accessible within the cluster, with GitLab communicating through the [Kubernetes API](https://kubernetes.io/docs/concepts/overview/kubernetes-api/).
@@ -45,9 +49,9 @@ CPU and Memory consumption is monitored, but requires [naming conventions](prome
 The [NGINX Ingress](../clusters/index.md#installing-applications) that is deployed by GitLab to clusters, is automatically annotated for monitoring providing key response metrics: latency, throughput, and error rates.
-## Manual configuration of Prometheus
-### Requirements
+### Manual configuration of Prometheus
+#### Requirements
 Integration with Prometheus requires the following:
@@ -56,7 +60,7 @@ Integration with Prometheus requires the following:
 1. Each metric must be have a label to indicate the environment
 1. GitLab must have network connectivity to the Prometheus server
-### Getting started
+#### Getting started
 Installing and configuring Prometheus to monitor applications is fairly straight forward.
@@ -64,7 +68,7 @@ Installing and configuring Prometheus to monitor applications is fairly straight
 1. Set up one of the [supported monitoring targets](prometheus_library/metrics.md)
 1. Configure the Prometheus server to [collect their metrics](https://prometheus.io/docs/operating/configuration/#scrape_config)
-### Configuration in GitLab
+#### Configuration in GitLab
 The actual configuration of Prometheus integration within GitLab is very simple.
 All you will need is the DNS or IP address of the Prometheus server you'd like
@@ -83,9 +87,9 @@ to integrate with.
 Once configured, GitLab will attempt to retrieve performance metrics for any
 environment which has had a successful deployment.
-GitLab will automatically scan the Prometheus server for known metrics and attempt to identify the metrics for a particular environment. The supported metrics and scan process is detailed in our [Prometheus Metric Library documentation](prometheus_library/metrics.html).
-[Learn more about monitoring environments.](../../../ci/environments.md#monitoring-environments)
+GitLab will automatically scan the Prometheus server for metrics from known serves like Kubernetes and NGINX, and attempt to identify individual environment. The supported metrics and scan process is detailed in our [Prometheus Metric Library documentation](prometheus_library/metrics.html). 
+You can view the performance dashboard for an environment by [clicking on the monitoring button](../../../ci/environments.md#monitoring-environments).
 ## Determining the performance impact of a merge
@@ -93,7 +97,7 @@ GitLab will automatically scan the Prometheus server for known metrics and attem
 > GitLab 9.3 added the [numeric comparison](https://gitlab.com/gitlab-org/gitlab-ce/issues/27439) of the 30 minute averages.
 > Requires [Kubernetes](prometheus_library/kubernetes.md) metrics
-Developers can view theperformance impact of their changes within the merge
+Developers can view the performance impact of their changes within the merge
 request workflow. When a source branch has been deployed to an environment, a sparkline and numeric comparison of the average memory consumption will appear. On the sparkline, a dot
 indicates when the current changes were deployed, with up to 30 minutes of
 performance data displayed before and after. The comparison shows the difference between the 30 minute average before and after the deployment. This information is updated after
@@ -109,7 +113,7 @@ Prometheus server.
 ## Troubleshooting
-If the "Attempting to load performance data" screen continues to appear, it could be due to:
+If the "No data found" screen continues to appear, it could be due to:
 - No successful deployments have occurred to this environment.
 - Prometheus does not have performance data for this environment, or the metrics