Service Mesh Observability: UI Visualization

Since Consul 1.9.0, Consul's built in UI includes a topology visualization to show a service's immediate connectivity at a glance. It is not intended as a replacement for dedicated monitoring solutions, but rather as a quick overview of the state of a service and its connections within the Service Mesh.

The topology visualization requires services to be using service mesh via sidecar proxies.

The visualization may optionally be configured to include a link to an external per-service dashboard. This is designed to provide convenient deep links to your existing monitoring or Application Performance Monitoring (APM) solution for each service. More information can be found in Configuring Dashboard URLs.

It is possible to configure the UI to fetch basic metrics from your metrics provider storage to augment the visualization as displayed below.

Consul has built-in support for overlaying metrics from a Prometheus backend. Alternative metrics providers may be supported using a new and experimental JavaScript API. See Custom Metrics Providers.

Kubernetes

If running Consul in Kubernetes, the Helm chart can automatically configure Consul's UI to display topology visualizations. See our Kubernetes observability docs for more information.

Configuring the UI To Display Metrics

To configure Consul's UI to fetch metrics there are two required configuration settings. These need to be set on each Consul Agent that is responsible for serving the UI. If there are multiple clients with the UI enabled in a datacenter for redundancy these configurations must be added to all of them.

We assume that the UI is already enabled by setting ui_config.enabled to true in the agent's configuration file.

To use the built-in Prometheus provider ui_config.metrics_provider must be set to prometheus.

The UI must query the metrics provider through a proxy endpoint. This simplifies deployment where Prometheus is not exposed externally to UI user's browsers.

To set this up, provide the URL that the Consul agent should use to reach the Prometheus server in ui_config.metrics_proxy.base_url. For example in Kubernetes, the Prometheus helm chart by default installs a service named prometheus-server so each Consul agent can reach it on http://prometheus-server (using Kubernetes' DNS resolution).

A full configuration to enable Prometheus is given below.

ui_config {  enabled = true  metrics_provider = "prometheus"  metrics_proxy {    base_url = "http://prometheus-server"  }}

ui:  enabled: true  metrics:    enabled: true # by default, this inherits from the value global.metrics.enabled    provider: "prometheus"    baseURL: http://prometheus-server

{  "ui_config": {    "enabled": true,    "metrics_provider": "prometheus",    "metrics_proxy": {      "base_url": "http://prometheus-server"    }  }}

Configuring Dashboard URLs

Since Consul's visualization is intended as an overview of your mesh and not a comprehensive monitoring tool, you can configure a service dashboard URL template which allows users to click directly through to the relevant service-specific dashboard in an external tool like Grafana or a hosted provider.

To configure this, you must provide a URL template in the agent configuration file for all agents that have the UI enabled. The template is essentially the URL to the external dashboard, but can have placeholder values which will be replaced with the service name, namespace and datacenter where appropriate to allow deep-linking to the relevant information.

An example with Grafana is shown below.

ui_config {  enabled = true  dashboard_url_templates {    service = "https://grafana.example.com/d/lDlaj-NGz/service-overview?orgId=1&var-service={{Service.Name}}&var-namespace={{Service.Namespace}}&var-partition={{Service.Partition}}&var-dc={{Datacenter}}"  }}

# The UI is enabled by default so this stanza is not required.ui:  enabled: true  # This configuration requires version 0.40.0 or later of the Helm chart.  dashboardURLTemplates:    service: "https://grafana.example.com/d/lDlaj-NGz/service-overview?orgId=1&var-service={{Service.Name}}&var-namespace={{Service.Namespace}}&var-dc={{Datacenter}}" # If you are using a version of the Helm chart older than 0.40.0, you must# configure the dashboard URL template using the `server.extraConfig` parameter# in the Helm chart's values file.server:  extraConfig: |    {      "ui_config": {        "dashboard_url_templates": {          "service": "https://grafana.example.com/d/lDlaj-NGz/service-overview?orgId=1&var-service={{ "{{" }}Service.Name}}&var-namespace={{ "{{" }}Service.Namespace}}&var-dc={{ "{{" }}Datacenter}}"        }      }    }

{  "ui_config": {    "enabled": true,    "dashboard_url_templates": {      "service": "https://grafana.example.com/d/lDlaj-NGz/service-overview?orgId=1\u0026var-service={{Service.Name}}\u0026var-namespace={{Service.Namespace}}\u0026var-partition={{Service.Partition}}\u0026var-dc={{Datacenter}}"    }  }}

Metrics Proxy

In many cases the metrics backend may be inaccessible to UI user's browsers or may be on a different domain and so subject to CORS restrictions. To make it simpler to serve the metrics to the UI in these cases, the Consul agent can proxy requests for metrics from the UI to the backend.

This is intended to simplify setup in test and demo environments. Careful consideration should be given towards using this in production.

The simplest configuration is described in Configuring the UI for metrics.

Metrics Proxy Security

The metrics proxy endpoint is internal and intended only for UI use. However by enabling it anyone with network access to the agent's API port may use it to access metrics from the backend.

If ACLs are not enabled, full access to metrics will be exposed to un-authenticated workloads on the network.

With ACLs enabled, the proxy endpoint requires a valid token with read access to all nodes and services (across all namespaces in Enterprise):

service_prefix "" {  policy = "read"}node_prefix "" {  policy = "read"}

{  "service_prefix": {    "": {      "policy": "read"    }  },  "node_prefix": {    "": {      "policy": "read"    }  }}

namespace_prefix "" {  service_prefix "" {    policy = "read"  }  node_prefix "" {    policy = "read"  }}

{  "namespace_prefix": {    "": {      "service_prefix": {        "": {          "policy": "read"        }      },      "node_prefix": {        "": {          "policy": "read"        }      }    }  }}

It's typical for most authenticated users to have this level of access in Consul as it's required for viewing the catalog or discovering services. If you use a Single Sign-On integration (Consul Enterprise) users of the UI can be automatically issued an ACL token with the privileges above to be allowed access to the metrics through the proxy.

Even with ACLs enabled, the proxy endpoint doesn't deeply understand the query language of the backend so there is no way it can enforce least-privilege access to only specific service-related metrics.

If you are not comfortable with all users of Consul having full access to the metrics backend, you should not use the proxy and find an alternative like using a custom provider that can query the metrics backend directly.

Path Allowlist

To limit exposure of the metrics backend, paths must be explicitly added to an allowlist to avoid exposing unintended parts of the API. For example with Prometheus, both the /api/v1/query_range and /api/v1/query endpoints are needed to load time-series and individual stats. If the proxy had the base_url set to http://prometheus-server then the proxy would also expose read access to several other endpoints such as /api/v1/status/config which includes all Prometheus configuration which might include sensitive information.

If you use the built-in prometheus provider the proxy is limited to the essential endpoints. The default value for metrics_proxy.path_allowlist is ["/api/v1/query_range", "/api/v1/query"] as required by the built-in prometheus provider .

If you use a custom provider that uses the metrics proxy, you'll need to explicitly set the allowlist based on the endpoints the provider needs to access.

Adding Headers

It is also possible to configure the proxy to add one or more headers to requests as they pass through. This is useful when the metrics backend requires authentication. For example if your metrics are shipped to a hosted provider, you could provision an API token specifically for the Consul UI and configure the proxy to add it as in the example below. This keeps the API token only visible to Consul operators in the configuration file while UI users can query the metrics they need without separately obtaining a token for that provider or having a token exposed to them that they might be able to use elsewhere.

ui_config {  enabled = true  metrics_provider = "example-apm"  metrics_proxy {    base_url = "https://example-apm.com/api/v1/metrics"    add_headers = [      {        name = "Authorization"        value = "Bearer <token>"      }    ]  }}

{  "ui_config": {    "enabled": true,    "metrics_provider": "example-apm",    "metrics_proxy": {      "base_url": "https://example-apm.com/api/v1/metrics",      "add_headers": [        {          "name": "Authorization",          "value": "Bearer \u003ctoken\u003e"        }      ]    }  }}

Custom Metrics Providers

Consul 1.9.0 includes a built-in provider for fetching metrics from Prometheus. To enable the UI visualization feature to work with other existing metrics stores and hosted services, we created a "metrics provider" interface in JavaScript. A custom provider may be written and the JavaScript file served by the Consul agent.

The template for a complete provider JavaScript file is given below.

(function () {  var provider = {    /**     * init is called when the provider is first loaded.     *     * options.providerOptions contains any operator configured parameters     * specified in the `metrics_provider_options_json` field of the Consul     * agent configuration file.     *     * Consul will provide:     *     * 1. A boolean field options.metrics_proxy_enabled to indicate whether the     *    agent has a metrics proxy configured.     *     * 2. A function options.fetch which is a thin wrapper around the browser's     *    [Fetch API](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API)     *    that prefixes any url with the url of Consul's internal metrics proxy     *    endpoint and adds your current Consul ACL token to the request     *    headers. Otherwise it functions like the browser's native fetch.     *     * The provider should throw an Exception if the options are not valid, for     * example because it requires a metrics proxy and one is not configured.     */    init: function(options) {},     /**     * serviceRecentSummarySeries should return time series for a recent time     * period summarizing the usage of the named service in the indicated     * datacenter. In Consul Enterprise a non-empty namespace is also provided.     *     * If these metrics aren't available then an empty series array may be     * returned.     *     * The period may (later) be specified in options.startTime and     * options.endTime.     *     * The service's protocol must be given as one of Consul's supported     * protocols e.g. "tcp", "http", "http2", "grpc". If it is empty or the     * provider doesn't recognize the protocol, it should treat it as "tcp" and     * provide basic connection stats.     *     * The expected return value is a JavaScript promise which resolves to an     * object that should look like the following:     *     *  {     *    // The unitSuffix is shown after the value in tooltips. Values will be     *    // rounded and shortened. Larger values will already have a suffix     *    // like "10k". The suffix provided here is concatenated directly     *    // allowing for suffixes like "mbps/kbps" by using a suffix of "bps".     *    // If the unit doesn't make sense in this format, include a     *    // leading space for example " rps" would show as "1.2k rps".     *    unitSuffix: " rps",     *     *    // The set of labels to graph. The key should exactly correspond to a     *    // property of every data point in the array below except for the     *    // special case "Total" which is used to show the sum of all the     *    // stacked graph values. The key is displayed in the tooltip so it     *    // should be human-friendly but as concise as possible. The value is a     *    // longer description that is displayed in the graph's key on request     *    // to explain exactly what the metrics mean.     *    labels: {     *      "Total": "Total inbound requests per second.",     *      "Successes": "Successful responses (with an HTTP response code ...",     *      "Errors": "Error responses (with an HTTP response code in the ...",     *    },     *     *    data: [     *      {     *        time: 1600944516286, // milliseconds since Unix epoch     *        "Successes": 1234.5,     *        "Errors": 2.3,     *      },     *      ...     *    ]     *  }     *     *  Every data point object should have a value for every series label     *  (except for "Total") otherwise it will be assumed to be "0".     */    serviceRecentSummarySeries: function(serviceDC, namespace, serviceName, protocol, options) {},     /**     * serviceRecentSummaryStats should return four summary statistics for a     * recent time period for the named service in the indicated datacenter. In     * Consul Enterprise a non-empty namespace is also provided.     *     * If these metrics aren't available then an empty array may be returned.     *     * The period may (later) be specified in options.startTime and     * options.endTime.     *     * The service's protocol must be given as one of Consul's supported     * protocols e.g. "tcp", "http", "http2", "grpc". If it is empty or the     * provider doesn't recognize it it should treat it as "tcp" and provide     * just basic connection stats.     *     * The expected return value is a JavaScript promise which resolves to an     * object that should look like the following:     *     *  {          // stats is an array of stats to show. The first four of these will be          // displayed. Fewer may be returned if not available.     *    stats: [     *      {     *        // label should be 3 chars or fewer as an abbreviation     *        label: "SR",     *     *        // desc describes the stat in a tooltip     *        desc: "Success Rate - the percentage of all requests that were not 5xx status",     *     *        // value is a string allowing the provider to format it and add     *        // units as appropriate. It should be as compact as possible.     *        value: "98%",     *      }     *    ]     *  }     */    serviceRecentSummaryStats: function(serviceDC, namespace, serviceName, protocol, options) {},     /**     * upstreamRecentSummaryStats should return four summary statistics for each     * upstream service over a recent time period, relative to the named service     * in the indicated datacenter. In Consul Enterprise a non-empty namespace     * is also provided.     *     * Note that the upstreams themselves might be in different datacenters but     * we only pass the target service DC since typically these metrics should     * be from the outbound listener of the target service in this DC even if     * the requests eventually end up in another DC.     *     * If these metrics aren't available then an empty array may be returned.     *     * The period may (later) be specified in options.startTime and     * options.endTime.     *     * The expected return value is a JavaScript promise which resolves to an     * object that should look like the following:     *     *   {     *     stats: {     *       // Each upstream will appear as an entry keyed by the upstream     *       // service name. The value is an array of stats with the same     *       // format as serviceRecentSummaryStats response.stats. Note that     *       // different upstreams might show different stats depending on     *       // their protocol.     *       "upstream_name": [     *         {label: "SR", desc: "...", value: "99%"},     *         ...     *       ],     *       ...     *     }     *   }     */    upstreamRecentSummaryStats: function(serviceDC, namespace, serviceName, upstreamName, options) {},     /**     * downstreamRecentSummaryStats should return four summary statistics for     * each downstream service over a recent time period, relative to the named     * service in the indicated datacenter. In Consul Enterprise a non-empty     * namespace is also provided.     *     * Note that the service may have downstreams in different datacenters. For     * some metrics systems which are per-datacenter this makes it hard to query     * for all downstream metrics from one source. For now the UI will only show     * downstreams in the same datacenter as the target service. In the future     * this method may be called multiple times, once for each DC that contains     * downstream services to gather metrics from each. In that case a separate     * option for target datacenter will be used since the target service's DC     * is still needed to correctly identify the outbound clusters that will     * route to it from the remote DC.     *     * If these metrics aren't available then an empty array may be returned.     *     * The period may (later) be specified in options.startTime and     * options.endTime.     *     * The expected return value is a JavaScript promise which resolves to an     * object that should look like the following:     *     *   {     *     stats: {     *       // Each downstream will appear as an entry keyed by the downstream     *       // service name. The value is an array of stats with the same     *       // format as serviceRecentSummaryStats response.stats. Different     *       // downstreams may display different stats if required although the     *       // protocol should be the same for all as it is the target     *       // service's protocol that matters here.     *       "downstream_name": [     *         {label: "SR", desc: "...", value: "99%"},     *         ...     *       ],     *       ...     *     }     *   }     */    downstreamRecentSummaryStats: function(serviceDC, namespace, serviceName, options) {}  }   // Register the provider with Consul for use. This example would be usable by  // configuring the agent with `ui_config.metrics_provider = "example-provider".  window.consul.registerMetricsProvider("example-provider", provider) }());

Additionally, the built in Prometheus provider code can be used as a reference.

Configuring the Agent With a Custom Metrics Provider.

In the example below, we configure the Consul agent to use a metrics provider named example-provider, which is defined in /usr/local/bin/example-metrics-provider.js. The name example-provider must have been specified in the call to consul.registerMetricsProvider as in the code listing in the last section.

ui_config {  enabled = true  metrics_provider = "example-provider"  metrics_provider_files = ["/usr/local/bin/example-metrics-provider.js"]  metrics_provider_options_json = <<-EOT    {      "foo": "bar"    }  EOT}

{  "ui_config": {    "enabled": true,    "metrics_provider": "example-provider",    "metrics_provide_files": ["/usr/local/bin/example-metrics-provider.js"],    "metrics_provider_options_json": "{\"foo\":\"bar\"}"  }}

More than one JavaScript file may be specified in metrics_provider_files and all will be served allowing flexibility if needed to include dependencies. Only one metrics provider can be configured and used at one time.

The metrics_provider_options_json field is an optional literal JSON object which is passed to the provider's init method at startup time. This allows configuring arbitrary parameters for the provider in config rather than hard coding them into the provider itself to make providers more reusable.

The provider may fetch metrics directly from another source although in this case the agent will probably need to serve the correct CORS headers to prevent browsers from blocking these requests. These may be configured with http_config.response_headers.

Alternatively, the provider may choose to use the built-in metrics proxy to avoid cross domain issues or to inject additional authorization headers without requiring each UI user to be separately authenticated to the metrics backend.

A function that behaves like the browser's Fetch API is provided to the metrics provider JavaScript during init as options.fetch. This is a thin wrapper that prefixes any url with the url of Consul's metrics proxy endpoint and adds your current Consul ACL token to the request headers. Otherwise it functions like the browser's native fetch and will forward your request on to the metrics backend. The response will be returned without any modification to be interpreted by the provider and converted into the format as described in the interface above.

Provider authors should make it clear to users which paths are required so they can correctly configure the path allowlist in the metrics proxy to avoid exposing more than needed of the metrics backend.

Custom Provider Security Model

Since the JavaScript file(s) are included in Consul's UI verbatim, the code in them must be treated as fully trusted by the operator. Typically they will have authored this or will need to carefully vet providers written by third parties.

This is equivalent to using the existing -ui-dir flag to serve an alternative version of the UI - in either model the operator takes full responsibility for the provenance of the code being served since it has the power to intercept ACL tokens, access cookies and local storage for the Consul UI domain and possibly more.

Current Limitations

Currently there are some limitations to this feature.

• No cross-datacenter support The initial metrics provider integration is with Prometheus which is popular and easy to setup within one Kubernetes cluster. However, when using the Consul UI in a multi-datacenter deployment, the UI allows users to select any datacenter to view.

  This means that the Prometheus server that the Consul agent serving the UI can access likely only has metrics for the local datacenter and a full solution would need additional proxying or exposing remote Prometheus servers on the network in remote datacenters. Later we may support an easy way to set this up via Consul service mesh but initially we don't attempt to fetch metrics in the UI if you are browsing a remote datacenter.

• Built-in provider requires metrics proxy Initially the built-in prometheus provider only support querying Prometheus via the metrics proxy. Later it may be possible to configure it for direct access to an expose Prometheus.