add documentation about prometheus (#61)

Signed-off-by: Augustin Husson <augustin.husson@amadeus.com>

docs/prometheus.md

@@ -0,0 +1,289 @@
+# Prometheus-related plugins
+
+This documentation provides the definition of the different plugins related to Prometheus.
+
+## Datasource
+
+```yaml
+kind: "PrometheusDatasource"
+spec: <prometheus_plugin_spec>
+```
+
+### Plugin Specification
+
+Prometheus as a datasource is basically an HTTP server. So we need to define an HTTP config.
+
+```yaml
+# It is the url of the datasource.
+# Leave it empty if you don't want to access the datasource directly from the UI.
+# You should define a proxy if you want to access the datasource through the Perses' server.
+directUrl: <url> # Optional
+
+# It is the http configuration that will be used by the Perses' server to redirect to the datasource any query sent by the UI.
+proxy: <HTTP Proxy specification> # Optional
+
+scrapeInterval: <duration> # Optional
+```
+
+#### HTTP Proxy specification
+
+```yaml
+kind: "HTTPProxy"
+spec:
+  # URL is the url of datasource. It is not the url of the proxy.
+  url: <url>
+
+  # It is a tuple list of http methods and http endpoints that will be accessible.
+  # Leave it empty if you don't want to restrict the access to the datasource.
+  allowedEndpoints:
+    - <Allowed Endpoints specification> # Optional
+
+  # It can be used to provide additional headers that need to be forwarded when requesting the datasource
+  headers:
+    <string>: <string> # Optional
+
+  # This is the name of the secret that should be used for the proxy or discovery configuration
+  # It will contain any sensitive information such as password, token, certificate.
+  # Please read the documentation about secrets to understand how to create one
+  secret: <string> # Optional
+```
+
+##### Allowed Endpoints specification
+
+```yaml
+endpointPattern: <RegExp>
+method: <enum | possibleValue = 'POST' | 'PUT' | 'PATCH' | 'GET' | 'DELETE'>
+```
+
+### Example
+
+A simple Prometheus datasource would be
+
+```yaml
+kind: "Datasource"
+metadata:
+  name: "PrometheusDemo"
+  project: "perses"
+spec:
+  default: true
+  plugin:
+    kind: "PrometheusDatasource"
+    spec:
+      directUrl: "https://prometheus.demo.do.prometheus.io"
+```
+
+A more complex one:
+
+```yaml
+kind: "Datasource"
+metadata:
+  name: "PrometheusDemo"
+  project: "perses"
+spec:
+  default: true
+  plugin:
+    kind: "PrometheusDatasource"
+    spec:
+      proxy:
+        kind: "HTTPProxy"
+        spec:
+          url: "https://prometheus.demo.do.prometheus.io"
+          allowedEndpoints:
+            - endpointPattern: "/api/v1/labels"
+              method: "POST"
+            - endpointPattern: "/api/v1/series"
+              method: "POST"
+            - endpointPattern: "/api/v1/metadata"
+              method: "GET"
+            - endpointPattern: "/api/v1/query"
+              method: "POST"
+            - endpointPattern: "/api/v1/query_range"
+              method: "POST"
+            - endpointPattern: "/api/v1/label/([a-zA-Z0-9_-]+)/values"
+              method: "GET"
+          secret: "prometheus_secret_config"
+```
+
+## Query
+
+Perses currently supports only one kind of query for Prometheus: `PrometheusTimeSeriesQuery`. Others will come in the future.
+
+```yaml
+kind: "PrometheusTimeSeriesQuery"
+spec: <Timeseries Query specification>
+```
+
+### Timeseries Query specification
+
+```yaml
+#`query` is the promQL expression.
+query: <string>
+
+# `datasource` is a datasource selector. If not provided, the default PrometheusDatasource is used.
+# See the documentation about the datasources to understand how it is selected.
+datasource: <Datasource selector> # Optional
+seriesNameFormat: <string> # Optional
+
+# `minStep` is the minimum time interval you want between each data points.
+minStep: <duration> # Optional
+resolution: number # Optional
+```
+
+#### Example
+
+A simple one:
+
+```yaml
+kind: "TimeSeriesQuery"
+spec:
+  plugin:
+    kind: "PrometheusTimeSeriesQuery"
+    spec:
+      query: "rate(caddy_http_response_duration_seconds_sum[$interval])"
+```
+
+## Variable
+
+### PrometheusLabelNamesVariable
+
+```yaml
+kind: "PrometheusLabelNamesVariable"
+spec: <Prometheus Label Names specification>
+```
+
+#### Prometheus Label Names specification
+
+```yaml
+# `datasource` is a datasource selector. If not provided, the default PrometheusDatasource is used.
+# See the documentation about the datasources to understand how it is selected.
+datasource: <datasource_selector> # Optional
+matchers:
+  - <string> # Optional
+```
+
+#### Example
+
+A simple Prometheus LabelNames variable would be
+
+```yaml
+kind: "Variable"
+metadata:
+  name: "labelNames"
+  project: "perses"
+spec:
+  kind: "ListVariable"
+  spec:
+    plugin:
+      kind: "PrometheusLabelNamesVariable"
+```
+
+A more complex one
+
+```yaml
+kind: "Variable"
+metadata:
+  name: "labelNames"
+  project: "perses"
+spec:
+  kind: "ListVariable"
+  spec:
+    allowMultiple: false
+    allowAllValue: false
+    plugin:
+      kind: "PrometheusLabelNamesVariable"
+      spec:
+        datasource:
+          kind: "PrometheusDatasource"
+          name: "PrometheusDemo"
+        matchers:
+          - "up"
+```
+
+### PrometheusLabelValuesVariable
+
+```yaml
+kind: "PrometheusLabelValuesVariable"
+spec: <Prometheus Label Values specification>
+```
+
+#### Prometheus Label Values specification
+
+```yaml
+# `datasource` is a datasource selector. If not provided, the default PrometheusDatasource is used.
+# See the documentation about the datasources to understand how it is selected.
+datasource: <Datasource selector> # Optional
+labelName: <string>
+matchers:
+  - <string> # Optional
+```
+
+#### Example
+
+A simple Prometheus LabelValues variable would be
+
+```yaml
+kind: "Variable"
+metadata:
+  name: "job"
+  project: "perses"
+spec:
+  kind: "ListVariable"
+  spec:
+    allowMultiple: false
+    allowAllValue: false
+    plugin:
+      kind: "PrometheusLabelValuesVariable"
+      spec:
+        labelName: "job"
+```
+
+A more complex one
+
+```yaml
+kind: "Variable"
+metadata:
+  name: "instance"
+  project: "perses"
+spec:
+  kind: "ListVariable"
+  spec:
+    allowMultiple: false
+    allowAllValue: false
+    plugin:
+      kind: "PrometheusLabelValuesVariable"
+      spec:
+        datasource:
+          kind: "PrometheusDatasource"
+          name: "PrometheusDemo"
+        labelName: "instance"
+        matchers:
+        - "up{job=~\"$job\"}"
+```
+
+### PrometheusPromQLVariable
+
+```yaml
+kind: "PrometheusPromQLVariable"
+spec: <Prometheus PromQL specification>
+```
+
+#### Prometheus PromQL specification
+
+```yaml
+# `datasource` is a datasource selector. If not provided, the default PrometheusDatasource is used.
+# See the documentation about the datasources to understand how it is selected.
+datasource: <Datasource selector> # Optional
+
+# The promql expression
+expr: <string>
+labelName: <string> # Optional
+```
+
+### Datasource selector
+
+```yaml
+kind: "PrometheusDatasource"
+
+# The name of the datasource regardless its level
+name: <string> # Optional
+```