Apache SkyWalking – Grafana

Blog: Build Grafana dashboards for Apache SkyWalking -- Native PromQL Support

Thu, 16 Mar 2023 00:00:00 +0000

Background

As an application performance monitoring tool for distributed systems, Apache SkyWalking provides monitoring, tracing, diagnosing capabilities for distributed system in Cloud Native architecture. Prometheus is an open-source systems monitoring and alerting toolkit with an active ecosystem. Especially Prometheus metrics receive widespread support through exporters and integrations. PromQL as Prometheus Querying Language containing a set of expressions and expose HTTP APIs to read metrics.

SkyWalking supports to ingest Prometheus metrics through OpenTelemetry collector and through the aggregate calculation of these metrics to provide a variety of systems monitoring, such as Linux Monitoring and Kubernetes monitoring. SkyWalking already provides native UI and GraphQL API for users. But as designed to provide wider ecological integration capabilities, since 9.4.0, it provides PromQL Service, the third-party systems or visualization platforms that already support PromQL (such as Grafana), could obtain metrics through it. SkyWalking users will benefit from it when they integrate with different systems.

What is PromQL Service in SkyWalking?

PromQL Service is a query engine on the top of SkyWalking native GraphQL query, with additional query stage calculation capabilities powered by Prometheus expressions. It can accept PromQL HTTP API requests, parse Prometheus expressions, and transform between Prometheus metrics and SkyWalking metrics.

The PromQL Service follows all PromQL’s protocols and grammar and users can use it as they would with PromQL. As SkyWalking is fundamentally different from Prometheus in terms of metric classification, format, storage, etc. PromQL Service doesn’t have to implement the full PromQL feature. Refer to the documentation for the detail.

SkyWalking Basic Concepts

Here are some basic concepts and differences from Prometheus that users need to understand in order to use the PromQL service: Prometheus metrics specify the naming format and structure, the actual metric names and labels are determined by the client provider, and the details are stored. The user aggregates and calculates the metrics using the expression in PromQL. Unlike Prometheus, SkyWalking’s metric mechanism is built around the following core concepts with a hierarchical structure:

Layer: represents an abstract framework in computer science, such as Operating System(OS_LINUX layer), Kubernetes(k8s layer). This layer would be the owner of different services detected from different technologies. All Layers definitions can be found here.
Service: Represents a set/group of workloads which provides the same behaviors for incoming requests.
Service Instance: An individual workload in the Service group.
Endpoint: A path in a service for incoming requests.
Process: An operating system process. In some scenarios, a service instance is not a process, such as a pod Kubernetes could contain multiple processes.

The metric name and properties (labels) are configured by the SkyWalking OAP server based on the data source as well as OAL and MAL. SkyWalking provides the ability to down-sampling time series metrics, and generate different time bucket data (minute, hour, day).

The SkyWalking metric stream is as follows:

Traffic

The metadata of the Service/ServiceRelation/Instance/ServiceInstanceRelation/Endpoint/EndpointRelation/Process/ProcessRelation. Include names, layers, properties, relations between them, etc.

Metric

Name: metric name, configuration from OAL and MAL.
Entity: represents the metrics’ belonging and used for the query. An Entity will contain the following information depending on the Scope： Scope represents the metrics level and in query stage represents the Scope catalog, Scope catalog provides high-dimension classifications for all scopes as a hierarchy structure.

Scope	Entity Info
Service	Service(include layer info)
ServiceInstance	Service, ServiceInstance
Endpoint	Service, Endpoint
ServiceRelation	Service, DestService
ServiceInstanceRelation	ServiceInstance, DestServiceInstance
EndpointRelation	Endpoint, DestEndpoint
Process	Service, ServiceInstance, Process
ProcessRelation	Process, ServiceInstance, DestProcess

Value:

single value: long.
labeled value: text, label1,value1|label2,value2|..., such as L2 aggregation,5000 | L1 aggregation,8000.

TimeBucket: the time is accurate to minute, hour, day.

How to use PromQL Service

Setup

PromQL Service is enabled by default after v9.4.0, so no additional configuration is required. The default ports, for example, can be configured by using OAP environment variables:

restHost: ${SW_PROMQL_REST_HOST:0.0.0.0}
restPort: ${SW_PROMQL_REST_PORT:9090}
restContextPath: ${SW_PROMQL_REST_CONTEXT_PATH:/}
restMaxThreads: ${SW_PROMQL_REST_MAX_THREADS:200}
restIdleTimeOut: ${SW_PROMQL_REST_IDLE_TIMEOUT:30000}
restAcceptQueueSize: ${SW_PROMQL_REST_QUEUE_SIZE:0}

Use Prometheus expression

PromQL matches metric through the Prometheus expression. Here is a typical Prometheus metric.

To match the metric, the Prometheus expression is as follows:

In the PromQL Service, these reserved labels would be parsed as the metric name and entity info fields with other labels for the query. The mappings are as follows.

SkyWalking Concepts	Prometheus expression
Metric name	Metric name
Layer	Label
Service	Label
ServiceInstance	Label<service_instance>
Endpoint	Label
…	…

For example, the following expressions are used to match query metrics: service_cpm, service_instance_cpm, endpoint_cpm

service_cpm{service='agent::songs', layer='GENERAL'}
service_instance_cpm{service='agent::songs', service_instance='agent::songs_instance_1', layer='GENERAL'}
endpoint_cpm{service='agent::songs', endpoint='GET:/songs', layer='GENERAL'}

Typical Query Example

At here, we take the SkyWalking Showcase deployment as the playground to demonstrate how to use PromQL for SkyWalking metrics.

The following examples can be used to query the metadata and metrics of services through PromQL Service.

Get metrics names

Query:

http://localhost:9099/api/v1/label/__name__/values

Result:

{
    "status": "success",
    "data": [
        "meter_mysql_instance_qps",
        "service_cpm",
        "envoy_cluster_up_rq_active",
        "instance_jvm_class_loaded_class_count",
        "k8s_cluster_memory_requests",
        "meter_vm_memory_used",
        "meter_apisix_sv_bandwidth_unmatched",
        "meter_vm_memory_total",
        ...
    ]
}

Select a metric and get the labels

Query:

http://localhost:9099/api/v1/labels?match[]=service_cpm

Result:

{
  "status": "success",
  "data": [
    "layer",
    "service",
    "top_n",
    "order"
  ]
}

Get services from a specific layer

Query:

http://127.0.0.1:9099/api/v1/series?match[]=service_traffic{layer='GENERAL'}&start=1677479336&end=1677479636

Result:

{
    "status": "success",
    "data": [
        {
            "__name__": "service_traffic",
            "service": "agent::songs",
            "scope": "Service",
            "layer": "GENERAL"
        },
        {
            "__name__": "service_traffic",
            "service": "agent::recommendation",
            "scope": "Service",
            "layer": "GENERAL"
        },
        {
            "__name__": "service_traffic",
            "service": "agent::app",
            "scope": "Service",
            "layer": "GENERAL"
        },
        {
            "__name__": "service_traffic",
            "service": "agent::gateway",
            "scope": "Service",
            "layer": "GENERAL"
        },
        {
            "__name__": "service_traffic",
            "service": "agent::frontend",
            "scope": "Service",
            "layer": "GENERAL"
        }
    ]
}

Query specific metric for a service

Query:

http://127.0.0.1:9099/api/v1/query?query=service_cpm{service='agent::songs', layer='GENERAL'}

Result:

{
  "status": "success",
  "data": {
    "resultType": "vector",
    "result": [
      {
        "metric": {
          "__name__": "service_cpm",
          "layer": "GENERAL",
          "scope": "Service",
          "service": "agent::songs"
        },
        "value": [
          1679559960,
          "6"
        ]
      }
    ]
  }
}

About the range query and different metrics type for query can refer to the document here.

Build Grafana Dashboard

From the above, we know the mechanism and how to query from PromQL Service, now we can build the Grafana Dashboard for the above service example. Note: All the following configurations are based on Grafana version 9.1.0.

SkyWalking Showcase provides dashboards files such as services of General and Service Mesh layers， we can quickly create a dashboard for the General layer service by importing the dashboard JSON file.

After the Grafana application is deployed, follow the steps below:

Configure Data Source

First, we need to create a data source: In the data source config panel, chose Prometheus and set the URL to the OAP server address, the default port is 9090. Here set the data source name SkyWalking in case there are multiple Prometheus data sources.

Import Dashboard File

Create a dashboard folder named SkyWalking.
Import the dashboard file into Grafana, there are two ways to get the file:
1. From SkyWalking Showcase.
2. Go to SkyWaking Demo: Preview metrics on Grafana, and export it from the General Service dashboard.
Done! Now we can see the dashboard is working, the services are in the drop-down list and the metrics are displayed on the panels.

This is an easy way to build, but we need to know how it works if we want to customize it.

How the dashboard works

Dashboard Settings

Open the Settings-Variables we can see the following variables:

Let’s look at what each variable does:

$DS_SkyWalking

This is a data source ty variable that specifies the Prometheus data source which was defined earlier as SkyWalking.
$layer

This is a constant type because in the ‘General Service’ dashboard, all services belong to the ‘GENERAL’ layer, so they can be used directly in each query Note When you customize other layers, this value must be defined in the Layer mentioned above.
$service

Query type variable, to get all service names under this layer for the drop-down list.

Query expression:
```
label_values(service_traffic{layer='$layer'}, service)
```
The query expression will query HTTP API /api/v1/series for service metadata in $layer and fetch the service name according to the label(service).
$service_instance

Same as the $service is a query variable that is used to select all instances of the service in the drop-down list.

Query expression:
```
label_values(instance_traffic{layer='$layer', service='$service'}, service_instance)
```
The query expression here not only specifies the $layer but also contains the variable $service, which is used to correlate with the services for the drop-down list.
$endpoint

Same as the $service is a query variable that is used to select all endpoints of the service in the drop-down list.

Query expression:
```
label_values(endpoint_traffic{layer='$layer', service='$service', keyword='$endpoint_keyword', limit='$endpoint_limit'}, endpoint)
```
The query expression here specifies the $layer and $service which are used to correlate with the services for the drop-down list. And also accept variables $endpoint_keyword and $endpoint_limit as filtering condition.
$endpoint_keyword

A text type variable that the user can input to filter the return value of $endpoint.
$endpoint_limit

Custom type, which the user can select to limit the maximum number of returned endpoints.

Panel Configurations

There are several typical metrics panels on this dashboard, let’s see how it’s configured.

Common Value Metrics

Select Time series chart panel Service Apdex and click edit.

Query expression
```
service_apdex{service='$service', layer='$layer'} / 10000
```
The metric scope is Service, add labels service and layer for the match, and the label value used the variables configured above. The calculation Divided by 10000 is used for matching the result units. The document for the query can refer to here.
Set Query options --> Min interval = 1m, because the metrics min time bucket in SkyWalking is 1m.
Set Connect null values --> Always and Show points --> Always because when the query interval > 1 hour or 1 day SkyWalking returns the hour/day step metrics values.

Labeled Value Metrics

Select Time series chart panel Service Response Time Percentile and click edit.

Query expression
```
service_percentile{service='$service', layer='$layer', labels='0,1,2,3,4', relabels='P50,P75,P90,P95,P99'}
```
The metric scope is Service, add labels service and layer for the match, and the label value used the variables configured above. Add labels='0,1,2,3,4' filter the result label, and addrelabels='P50,P75,P90,P95,P99' rename the result label. The document for the query can refer to here.
Set Query options --> Min interval = 1m, because the metrics min time bucket in SkyWalking is 1m.
Set Connect null values --> Always and Show points --> Always because when the query interval > 1 hour or 1 day SkyWalking returns the hour/day step metrics values.
Set Legend to {{label}} for show up.

Sort Metrics

Select Time series chart panel Service Response Time Percentile and click edit.

Query expression
```
service_instance_cpm{parent_service='$service', layer='$layer', top_n='10', order='DES'}
```
The expression is used for query the sore metrics under service, so add labels parent_service and layer for the match. Add top_n='10' and order='DES' filter the result. The document for the query can refer to here.
Set Query options --> Min interval = 1m, because the metrics min time bucket in SkyWalking is 1m.
Set the Calculation --> Latest*.
Set Legend to {{service_instance}} for show up.

Conclusion

In this article, we introduced what is the PromQL Service in SkyWalking and its background. Detailed how to use PromQL Service and the basic concepts related to SkyWalking, and show how to use PromQL Service to build Grafana dashboards for SkyWalking.

In the future, there will be more integrations by leveraging this protocol, such as CI/CD, HPA (scaling), etc.

Zh: 为 Apache SkyWalking 构建 Grafana Dashboard —— 原生 PromQL 支持

Thu, 16 Mar 2023 00:00:00 +0000

背景

Apache SkyWalking 作为分布式系统的应用性能监控工具，提供了对云原生架构下的分布式系统的监控、跟踪、诊断能力。Prometheus 是一个开源系统监控和警报工具包，具有活跃的生态系统。特别是 Prometheus 指标通过导出器和集成得到广泛支持。 PromQL 作为 Prometheus 查询语言，包含一组表达式并公开 HTTP API 以读取指标。

SkyWalking 支持通过 OpenTelemetry 收集器摄取 Prometheus 指标，并通过这些指标的聚合计算提供多种系统监控，例如 Linux 监控和 Kubernetes 监控。SkyWalking 已经为用户提供了原生 UI 和 GraphQL API。但为了提供更广泛的生态整合能力，从 9.4.0 开始，它提供了 PromQL 服务，已经支持 PromQL 的第三方系统或可视化平台（如 Grafana），可以通过它获取指标。SkyWalking 用户在与不同系统集成时将从中受益。

SkyWalking 中的 PromQL 服务是什么？

PromQL 服务是 SkyWalking 原生 GraphQL 查询之上的查询引擎，具有由 Prometheus 表达式提供支持的附加查询阶段计算能力。它可以接受 PromQL HTTP API 请求，解析 Prometheus 表达式，并在 Prometheus 指标和 SkyWalking 指标之间进行转换。

PromQL 服务遵循 PromQL 的所有协议和语法，用户可以像使用 PromQL 一样使用它。由于 SkyWalking 在度量分类、格式、存储等方面与 Prometheus 有根本不同，因此 PromQL 服务不必实现完整的 PromQL 功能。有关详细信息，请参阅文档。

SkyWalking 基本概念

以下是用户使用 PromQL 服务需要了解的一些基本概念和与 Prometheus 的区别： Prometheus 指标指定命名格式和结构，实际指标名称和标签由客户端提供商确定，并存储详细信息。用户使用 PromQL 中的表达式聚合和计算指标。与 Prometheus 不同，SkyWalking 的度量机制是围绕以下具有层次结构的核心概念构建的：

层（Layer）：表示计算机科学中的一个抽象框架，如 Operating System（OS_LINUX 层）、Kubernetes（k8s 层）。该层将是从不同技术检测到的不同服务的所有者。可以在此处

找到所有层定义。
服务：表示一组 / 一组工作负载，它为传入请求提供相同的行为。
服务实例：服务组中的单个工作负载。
端点：传入请求的服务路径。
进程：操作系统进程。在某些场景下，service instance 不是一个进程，比如一个 Kubernetes Pod 可能包含多个进程。

Metric 名称和属性（标签）由 SkyWalking OAP 服务器根据数据源以及 OAL 和 MAL 配置。SkyWalking 提供了对时间序列指标进行下采样（down-sampling），并生成不同时间段数据（分钟、小时、天）的能力。

SkyWalking 指标流如下：

流量

Service/ServiceRelation/Instance/ServiceInstanceRelation/Endpoint/EndpointRelation/Process/ProcessRelation 的元数据。包括名称、层、属性、它们之间的关系等。

指标

名称（Name）：指标名称，来自 OAL 和 MAL 的配置。
实体（Entity）：表示指标的归属，用于查询。一个 Entity 根据 Scope 不同会包含如下信息： Scope 代表指标级别，在查询阶段代表 Scope catalog，Scope catalog 为所有的 scope 提供了高维的分类，层次结构。

Scope	实体信息
Service	服务（包括图层信息）
ServiceInstance	服务、服务实例
Endpoint	服务、端点
ServiceRelation	服务，目标服务
ServiceInstanceRelation	服务实例、目标服务实例
EndpointRelation	端点、目标端点
Process	服务、服务实例、流程
ProcessRelation	进程、服务实例、DestProcess

值：

单值：long
标签值：文本，label1,value1|label2,value2|... ，例如 L2 aggregation,5000 | L1 aggregation,8000

TimeBucket：时间精确到分钟、小时、天

如何使用 PromQL 服务

设置

PromQL 服务在 v9.4.0 之后默认开启，不需要额外配置。例如，可以使用 OAP 环境变量配置默认端口：

restHost: ${SW_PROMQL_REST_HOST:0.0.0.0}
restPort: ${SW_PROMQL_REST_PORT:9090}
restContextPath: ${SW_PROMQL_REST_CONTEXT_PATH:/}
restMaxThreads: ${SW_PROMQL_REST_MAX_THREADS:200}
restIdleTimeOut: ${SW_PROMQL_REST_IDLE_TIMEOUT:30000}
restAcceptQueueSize: ${SW_PROMQL_REST_QUEUE_SIZE:0}

使用 Prometheus 表达式

PromQL 通过 Prometheus 表达式匹配指标。这是一个典型的 Prometheus 指标。

为了匹配指标，Prometheus 表达式如下：

在 PromQL 服务中，这些保留的标签将被解析为度量名称和实体信息字段以及用于查询的其他标签。映射如下。

SkyWalking 概念	Prometheus 表达
指标名称	指标名称
层	标签
服务	标签
服务实例	标签 <服务实例>
端点	标签
……	……

例如，以下表达式用于匹配查询指标：service_cpm、service_instance_cpm、endpoint_cpm

service_cpm {service='agent::songs', layer='GENERAL'}
service_instance_cpm {service='agent::songs', service_instance='agent::songs_instance_1', layer='GENERAL'}
endpoint_cpm {service='agent::songs', endpoint='GET:/songs', layer='GENERAL'}

典型查询示例

在这里，我们将 SkyWalking Showcase 部署作为 Playground 来演示如何使用 PromQL 获取 SkyWalking 指标。

以下示例可用于通过 PromQL 服务查询服务的元数据和指标。

获取指标名称

查询：

http://localhost:9099/api/v1/label/__name__/values

结果：

{
    "status": "success",
    "data": [
        "meter_mysql_instance_qps",
        "service_cpm",
        "envoy_cluster_up_rq_active",
        "instance_jvm_class_loaded_class_count",
        "k8s_cluster_memory_requests",
        "meter_vm_memory_used",
        "meter_apisix_sv_bandwidth_unmatched",
        "meter_vm_memory_total",
        ...
    ]
}

选择一个指标并获取标签

查询：

http://localhost:9099/api/v1/labels?match []=service_cpm

结果：

{
  "status": "success",
  "data": [
    "layer",
    "service",
    "top_n",
    "order"
  ]
}

从特定层获取服务

查询：

http://127.0.0.1:9099/api/v1/series?match []=service_traffic {layer='GENERAL'}&start=1677479336&end=1677479636

结果：

{
    "status": "success",
    "data": [
        {"__name__": "service_traffic",
            "service": "agent::songs",
            "scope": "Service",
            "layer": "GENERAL"
        },
        {"__name__": "service_traffic",
            "service": "agent::recommendation",
            "scope": "Service",
            "layer": "GENERAL"
        },
        {"__name__": "service_traffic",
            "service": "agent::app",
            "scope": "Service",
            "layer": "GENERAL"
        },
        {"__name__": "service_traffic",
            "service": "agent::gateway",
            "scope": "Service",
            "layer": "GENERAL"
        },
        {"__name__": "service_traffic",
            "service": "agent::frontend",
            "scope": "Service",
            "layer": "GENERAL"
        }
    ]
}

查询服务的特定指标

查询：

http://127.0.0.1:9099/api/v1/query?query=service_cpm {service='agent::songs', layer='GENERAL'}

结果：

{
  "status": "success",
  "data": {
    "resultType": "vector",
    "result": [
      {"metric": {
          "__name__": "service_cpm",
          "layer": "GENERAL",
          "scope": "Service",
          "service": "agent::songs"
        },"value": [
          1679559960,
          "6"
        ]
      }
    ]
  }
}

关于range query和不同的metrics type for query 可以参考这里的文档。

构建 Grafana Dashboard

从上面我们知道了 PromQL 服务的机制和查询方式，现在我们可以为上面的服务示例构建 Grafana Dashboard。注：以下所有配置均基于 Grafana 9.1.0 版本。

SkyWalking Showcase 提供了 General Service 和 Service Mesh 层等 Dashboard 文件，我们可以通过导入 Dashboard JSON 文件快速为层服务创建 Dashboard。

部署 Grafana 应用程序后，请按照以下步骤操作：

配置数据源

首先，我们需要创建一个数据源：在数据源配置面板中，选择 Prometheus 并设置 URL 为 OAP 服务器地址，默认端口为 9090。 SkyWalking 如果有多个 Prometheus 数据源，请在此处设置数据源名称。

导入 Dashboard 文件

创建一个名为 SkyWalking 的 Dashboard 文件夹。
将 Dashboard 文件导入到 Grafana 中，有两种获取文件的方式：
1. 来自 SkyWalking Showcase
2. 转到 SkyWaking Demo：在 Grafana 上预览指标，并将其从 General Service Dashboard 导出。
完毕！现在我们可以看到 Dashboard 正在运行，服务位于下拉列表中，指标显示在面板上。

这是一种简单的构建方式，但是如果我们想要自定义它，我们需要知道它是如何工作的。

Dashboard 的工作原理

Dashboard 设置

打开 Settings-Variables 我们可以看到如下变量：

让我们看看每个变量的作用：

$DS_SkyWalking

这是一个数据源 ty 变量，它指定了之前定义为 SkyWalking 的 Prometheus 数据源。
$layer

这是一个常量类型，因为在 ‘General Service’ Dashboard 中，所有服务都属于 ‘GENERAL’ 层，因此可以在每个查询中直接使用它们。注意，当您自定义其他层时，必须在 Layer 上面定义该值。
$service

查询类型变量，为下拉列表获取该层下的所有服务名称。

查询表达式：
```
label_values (service_traffic {layer='$layer'}, service)
```
查询表达式将查询 HTTP API /api/v1/series，以获取 $layer 中服务元数据，并根据标签（服务）提取服务名称。
$service_instance

与 $service 一样，是一个查询变量，用于在下拉列表中选择服务的所有实例。

查询表达式：
```
label_values (instance_traffic {layer='$layer', service='$service'}, service_instance)
```
这里的查询表达式不仅指定了 $layer 还包含 $service 变量，用于关联下拉列表的服务。
$endpoint

与 $service 一样，是一个查询变量，用于在下拉列表中选择服务的所有端点。

查询表达式：
```
label_values (endpoint_traffic {layer='$layer', service='$service', keyword='$endpoint_keyword', limit='$endpoint_limit'}, endpoint)
```
此处的查询表达式指定 $layer 和 $service 用于与下拉列表的服务相关联的。并且还接受 $endpoint_keyword 和 $endpoint_limit 变量作为过滤条件。
$endpoint_keyword

一个文本类型的变量，用户可以输入它来过滤 $endpoint 的返回值。
$endpoint_limit

自定义类型，用户可以选择它以限制返回端点的最大数量。

Dashboard 配置

这个 Dashboard 上有几个典型的指标面板，让我们看看它是如何配置的。

普通值指标

选择 Time series chart 面板 Service Apdex 并单击 edit。

查询表达式
```
service_apdex {service='$service', layer='$layer'} / 10000
```
指标范围为 Service，添加 service 和 layer 标签用于匹配，label 值使用上面配置的变量。该计算 Divided by 10000 用于匹配结果单位。查询文档可以参考这里。
设置 Query options --> Min interval = 1m，因为 SkyWalking 中的指标最小时间段是 1m。
设置 Connect null values --> AlwaysShow points --> Always，因为当查询间隔大于 1 小时或 1 天时，SkyWalking 返回小时 / 天步长指标值。

标签值指标

选择 Time series chart 面板 Service Response Time Percentile 并单击 edit。

查询表达式
```
service_percentile {service='$service', layer='$layer', labels='0,1,2,3,4', relabels='P50,P75,P90,P95,P99'}
```
指标范围为 Service，添加 service 和 layer 标签用于匹配，label 值使用上面配置的变量。添加 labels='0,1,2,3,4' 过滤结果标签，并添加 relabels='P50,P75,P90,P95,P99' 重命名结果标签。查询文档可以参考这里。
设置 Query options --> Min interval = 1m，因为 SkyWalking 中的指标最小时间段是 1m。
设置 Connect null values --> AlwaysShow points --> Always，因为当查询间隔 > 1 小时或 1 天时，SkyWalking 返回小时 / 天步长指标值。
设置 Legend 为 {{label}} 来展示。

排序指标

选择 Time series chart 面板 Service Response Time Percentile 并单击 edit。

查询表达式
```
service_instance_cpm {parent_service='$service', layer='$layer', top_n='10', order='DES'}
```
该表达式用于查询服务下的排序指标，因此添加标签 parent_service 和 layer 进行匹配。添加 top_n='10' 和 order='DES' 过滤结果。查询文档可以参考这里。
设置 Query options --> Min interval = 1m，因为 SkyWalking 中的指标最小时间段是 1m。
设置 Calculation --> Latest*。
设置 Legend 为 {{service_instance}} 来展示。

结论

在这篇文章中，我们介绍了 SkyWalking 中的 PromQL 服务是什么以及它的背景。详细介绍了 PromQL 服务的使用方法和 SkyWalking 相关的基本概念，展示了如何使用 PromQL 服务为 SkyWalking 构建 Grafana Dashboard。

未来，将会有更多的集成利用这个协议，比如 CI/CD、HPA（缩放）等。