diff --git a/site/plugins.md b/site/plugins.md index e04be905ae..126ffcd899 100644 --- a/site/plugins.md +++ b/site/plugins.md @@ -5,39 +5,67 @@ menu_order: 80 The following topics are discussed: - * [Listening Protocol](#listening-protocol) - * [Reporting](#reporting) - * [Interfaces](#interfaces) + * [Official Plugins](#official-plugins) + * [How Plugins Communicate with Scope](#plugins-internals) + * [Plugin IDs](#plugin-id) + * [Registering Plugins](#plugin-registration) + * [Reporter Interface](#reporter-interface) + * [Controller Interface](#controller-interface) + * [Control](#control) + * [How to Expose Controls](#expose-controls) + * [Naming Nodes](#naming-nodes) + * [A Guide to Developing Plugins](#plugins-developing-guide) + * [Setting up the Structure](#structure) + * [Defining the Reporter Interface](#reporter-interface) -With a Scope probe plugin, you can insert custom metrics into Scope and have them display in the user interface together with the Scope's standard set of metrics. +Any kind of metrics can be generated and inserted into Scope using custom plugins. Metrics generated through your plugin are displayed in the user interface alongside the standard set of metrics that are found in Weave Scope. ![Custom Metrics With Plugins](images/plugin-features.png) -You can find some examples in [the example plugins](https://github.com/weaveworks/scope/tree/master/examples/plugins) directory. +## Official Plugins -There are currently two different examples: +Official Weave Scope plugins can be found at [Weaveworks Plugins](https://github.com/weaveworks-plugins). -* A [Python plugin](https://github.com/weaveworks/scope/tree/master/examples/plugins/http-requests) using [bcc](http://iovisor.github.io/bcc/) to extract incoming HTTP request rates per process, without any application-level instrumentation requirements and negligible performance toll (metrics are obtained in-kernel without any packet copying to userspace). +* [IOWait](https://github.com/weaveworks-plugins/scope-iowait): is a Go plugin that uses [iostat](https://en.wikipedia.org/wiki/Iostat) to provide host-level CPU IO wait or idle metrics. ->**Note:** This plugin needs a [recent kernel version with ebpf support](https://github.com/iovisor/bcc/blob/master/INSTALL.md#kernel-configuration). It will not compile on current [dlite](https://github.com/nlf/dlite) and boot2docker hosts. +* [HTTP Statistics](https://github.com/weaveworks-plugins/scope-http-statistics): is a Python plugin that uses [bcc](http://iovisor.github.io/bcc/) to track multiple metrics about HTTP per process. It does this without any application-level instrumentation requirements and without a negligible performance toll. This plugin is a work in progress, and currently implements the following (for more information read the [plugin documentation](https://github.com/weaveworks-plugins/scope-http-statistics)): + * Number of HTTP requests per seconds. + * Number of HTTP responses code per second (per code). - * A [Go plugin](https://github.com/weaveworks/scope/tree/master/examples/plugins/iovisor), using [iostat](https://en.wikipedia.org/wiki/Iostat) to provide host-level CPU IO wait metrics. +> **Note:** The HTTP Statistics plugin requires a [recent kernel version with ebpf support](https://github.com/iovisor/bcc/blob/master/INSTALL.md#kernel-configuration) and it will not compile on [dlite](https://github.com/nlf/dlite) or on boot2docker hosts. -The example plugins are run by calling `make` in their directory. This builds the plugin, and immediately runs it in the foreground. To run the plugin in the background, see the `Makefile` for examples of the `docker run ...` command. +* [Traffic Control](https://github.com/weaveworks-plugins/scope-traffic-control): This plugin allows you to modify latency and packet loss for a specific container via controls from the container's detailed view in the Scope user interface. -If the running plugin was picked up by Scope, you will see it in the list of `PLUGINS` in the bottom right of the UI. +* [Volume Count](https://github.com/weaveworks-plugins/scope-volume-count): This plugin (written in Python) requests the number of mounted volumes for each container, and provides a container-level count. -## Listening Protocol +>**Note:**Installed and running plugins are shown in the list of `PLUGINS` in the bottom right of the Scope UI. -All plugins must listen for HTTP connections on a Unix socket in the `/var/run/scope/plugins` directory. The Scope probe recursively scans that directory every 5 seconds, to look for any sockets being added (or removed). It is also valid to put the plugin Unix socket into a sub-directory, in case you want to apply some permissions, or store any other information with the socket. +## How Plugins Communicate with Scope -When a new plugin is detected, the scope probe begins requesting reports from it via `GET /report`. +In this section how the different components of a plugin communicate with Scope are described. You can also find practical examples of how plugins work in the [Weaveworks Plugins](https://github.com/weaveworks-plugins) repositories. -All plugin endpoints are expected to respond within 500ms, and respond in the JSON format. +### Plugin IDs -### Reporting +Each plugin must have a unique ID and this ID must not change +during the plugin's lifetime. Scope probes retrieve the plugin's ID +from the plugin's socket filename. For example, if a socket is named +`my-plugin.sock`, the scope probe deduces the ID as +`my-plugin`. IDs may contain only alphanumeric sequences that are optionally +separated by a dash. -When the Scope probe discovers a new plugin Unix socket, it begins to periodically make a `GET` request to the `/report` endpoint. The report data structure returned from this will be merged into the probe's report and sent to the app. An example of the report structure can be viewed at the `/api/report` endpoint of any Scope app. +### Registering Plugins + +All plugins listen for HTTP connections on a UNIX socket in the `/var/run/scope/plugins` directory. The Scope probe recursively scans that directory every 5 seconds and looks for any added or removed sockets. + +If you want to run permissions or store any other information with the socket, you can also put the plugin UNIX socket into a sub-directory. + +When a new plugin is detected, the Scope probe begins requesting reports from it via `GET /report`. It is therefore important that **every plugin implements the report interface**. Implementing the report interface also means handling specific requests. + +All plugin endpoints are expected to respond within 500ms, and **must** respond using the JSON format. + +### Reporter Interface + +When a Scope probe discovers a new plugin UNIX socket, it begins to periodically make a `GET` request to the `/report` endpoint. The report data structure returned from this is merged into the probe's report and sent to the app. An example of the report structure can be viewed at the `/api/report` endpoint of any Scope app. In addition to any data about the topology nodes, the report returned from the plugin must include some metadata about the plugin itself. @@ -45,12 +73,12 @@ For example: ```json { - "Processes": {}, + ..., "Plugins": [ { - "id": "iowait", - "label": "IOWait", - "description": "Adds a graph of CPU IO Wait to hosts", + "id": "plugin-id", + "label": "Human Friendly Name", + "description": "Plugin's brief description", "interfaces": ["reporter"], "api_version": "1", } @@ -58,21 +86,311 @@ For example: } ``` -> **Note:** The `Plugins` section includes exactly one plugin description. The plugin description fields are: `interfaces` including `reporter`. +> **Note:** The `Plugins` section includes exactly one plugin description that displays in the UI. The other plugin fields are: + +* `id` - checks for duplicate plugins. It is required. +* `label` - a human readable label displayed in the UI. It is required. +* `description` - displayed in the UI. It is required. +* `interfaces` - a list of interfaces that the plugin supports. It is required, and must contain at least `["reporter"]`. +* `api_version` - ensure both the plugin and the scope probe can speak to each other. It is required, and must match the probe's value. + +### Controller Interface + +Plugins _may_ also implement the controller interface. Implementing the +controller interface means that the plugin can react to HTTP `POST` +control requests sent by the app. The plugin receives them only +for the controls it exposed in its reports. All such requests come to the +`/control` endpoint. + +Add the "controller" string to the interfaces field in the plugin specification. + +#### Control + +The `POST` requests contain a JSON-encoded body with the following: + +```json +{ + "AppID": "some ID of an app", + "NodeID": "an ID of the node that had the control activated", + "Control": "the name of the activated control" +} +``` + +The body of the response should also be JSON-encoded data. In most cases, +the body is an empty JSON object (so, "{}" after +serialization). If an error occurs when handling the control, +then the plugin sends a response with an `error` field set, for +example: + +```json +{ + "error": "An error message here" +} +``` + +Sometimes the control activation can make the control obsolete, and so the +plugin may want to hide it (for example, control for stopping the +container should be hidden after the container is stopped). For this +to work, the plugin sends a shortcut report by filling the +`ShortcutReport` field in the response, like so: + +```json +{ + "ShortcutReport": { body of the report here } +} +``` + +#### How to Expose Controls + +Each topology in the report (be it host, pod, endpoint and so on) contains +a set of available controls that a node in the topology may want to +show. The following (rather artificial) example shows a topology with +two controls (`ctrl-one` and `ctrl-two`) and two nodes, each with a different control defined: + +```json +{ + "Host": { + "controls": { + "ctrl-one": { + "id": "ctrl-one", + "human": "Ctrl One", + "icon": "fa-futbol-o", + "rank": 1 + }, + "ctrl-two": { + "id": "ctrl-two", + "human": "Ctrl Two", + "icon": "fa-beer", + "rank": 2 + } + }, + "nodes": { + "host1": { + "latestControls": { + "ctrl-one": { + "timestamp": "2016-07-20T15:51:05Z01:00", + "value": { + "dead": false + } + } + } + }, + "host2": { + "latestControls": { + "ctrl-two": { + "timestamp": "2016-07-20T15:51:05Z01:00", + "value": { + "dead": false + } + } + } + } + } + } +} +``` + +When control "ctrl-one" is activated, the plugin receives a +request as follows: + +```json +{ + "AppID": "some ID of an app", + "NodeID": "host1", + "Control": "ctrl-one" +} +``` + +A short note about the "icon" field of the topology control - the +value for it can be taken from [Font Awesome +Cheatsheet](http://fontawesome.io/cheatsheet/) + +#### Naming Nodes + +Often the controller plugin may want to add controls to already +existing nodes (for example add controls for network traffic management to nodes +representing the running Docker container). To achieve that, it is +important to make sure that the node ID in the plugin's report matches +the ID of the node created by the probe. The ID is a +semicolon-separated list of strings. -The fields are: +For containers, images, hosts and others, the ID is usually formatted +as `${name};<${tag}>`. The `${name}` variable is usually a name of a +thing the node represents, like an ID of the Docker container or the +hostname. The `${tag}` denotes the type of the node. -* `id` is used to check for duplicate plugins. It is required. -* `label` is a human readable plugin label displayed in the UI. It is required. -* `description` is displayed in the UI -* `interfaces` is a list of interfaces which this plugin supports. It is required, and must equal `["reporter"]`. -* `api_version` is used to ensure both the plugin and the scope probe can speak to each other. It is required, and must match the probe. +There is a fixed set of tags used by the probe: -### Interfaces +- `host` +- `container` +- `container_image` +- `pod` +- `service` +- `deployment` +- `replica_set` -Currently the only interface a plugin can fulfill is `reporter`. +These are examples of "tagged" node names: + +- The Docker container with full ID + 2299a2ca59dfd821f367e689d5869c4e568272c2305701761888e1d79d7a6f51: + `2299a2ca59dfd821f367e689d5869c4e568272c2305701761888e1d79d7a6f51;` +- The Docker image with name `docker.io/alpine`: + `docker.io/alpine;` +- The host with name `example.com`: `example.com;` + +The fixed set of tags listed above is not a complete set of names a +node can have though. For example, nodes representing processes +have IDs formatted as `${host};${pid}`. The easiest way to +discover how the nodes are named are: + + 1. Read the code in + [report/id.go](https://github.com/weaveworks/scope/blob/master/report/id.go). + 2. Browse the Weave Scope GUI, select some node and search for an `id` + key in the `nodeDetails` array in the address bar. + - For example in the + `http://localhost:4040/#!/state/{"controlPipe":null,"nodeDetails":[{"id":"example.com;","label":"example.com","topologyId":"hosts"}],…` + URL, you can find the `example.com;` which is an ID of the node + representing the host. + 3. Mentally substitute the `` with `/`. This can appear in + Docker image names, so `docker.io/alpine` in the address bar will + be `docker.ioalpine`. + + +## A Guide to Developing Plugins + +This section explains how to develop a simple plugin in Go. The code used here is a simplified version of the [Scope IOWait](https://github.com/weaveworks-plugins/scope-iowait) plugin. + +### Setting up the Structure + +As stated in the previous section, plugins need to be put into the `/var/run/scope/plugins` socket directory to be able to communicate with Scope. The best practice is to put the socket into a sub-directory and name it with the plugin ID (for example, `/var/run/scope/plugins/plugins-id/plugins-id.sock`). This is useful because the plugin can set more restrictive permissions to avoid unauthorized access as well as store other information along with the socket if needed. + +Example of a helper function for setting up the socket: + +```go +func setupSocket(socketPath string) (net.Listener, error) { + os.RemoveAll(filepath.Dir(socketPath)) + if err := os.MkdirAll(filepath.Dir(socketPath), 0700); err != nil { + return nil, fmt.Errorf("failed to create directory %q: %v", filepath.Dir(socketPath), err) + } + listener, err := net.Listen("unix", socketPath) + if err != nil { + return nil, fmt.Errorf("failed to listen on %q: %v", socketPath, err) + } + + log.Printf("Listening on: unix://%s", socketPath) + return listener, nil +} +``` + +Because Scope detects running plugins by looking into the `/var/run/scope/plugins` directory, plugins should remove their socket and the directory (if created) when they exit. The side effect of not doing that is that the Scope UI will show that a plugin is running but that it is not reachable. + +To remove the socket, and the directory, you can use the following helper function: + +```go +func setupSignals(socketPath string) { + interrupt := make(chan os.Signal, 1) + signal.Notify(interrupt, os.Interrupt, syscall.SIGTERM) + go func() { + <-interrupt + os.RemoveAll(filepath.Dir(socketPath)) + os.Exit(0) + }() +} +``` + +Also add the following to the main function the following: + +```golang +defer func() { + os.RemoveAll(filepath.Dir(socketPath)) + }() +``` + +This ensures that when the plugin terminates because of an error or an interrupt command, the `/var/run/scope/plugins/plugins-id` directory will be removed. + +A bare minimum boilerplate can be the following: + +```go +package main + +import ( + syscall +) + +func main() { + const socketPath = "/var/run/scope/plugins/my-plugin/my-plugin.sock" + setupSignals(socketPath) + + listener, err := setupSocket(socketPath) + + plugin := &Plugin{} + http.HandleFunc("/report", plugin.Report) + + defer func() { + listener.Close() + os.RemoveAll(filepath.Dir(socketPath)) + }() +} + +``` + +### Defining the Reporter Interface + +As stated in the [How Plugins Communicate with Scope](#plugins-internals) section, the reporter interface is mandatory. +Implementing the reporter interface means handling `GET /report` requests. + +The following code snippet is sufficient to implement it: + +```go +// Plugin groups the methods a plugin needs +type Plugin struct { + lock sync.Mutex +} + +type report struct { + Plugins []pluginSpec +} + +func (p *Plugin) makeReport() (*report, error) { + rpt := &report{ + Plugins: []pluginSpec{ + { + ID: "plugin-id", + Label: "Plugin Name", + Description: "Plugin short description", + Interfaces: []string{"reporter"}, + APIVersion: "1", + }, + }, + } + return rpt, nil +} + +// Report is called by scope when a new report is needed. It is part of the +// "reporter" interface, which all plugins must implement. +func (p *Plugin) Report(w http.ResponseWriter, r *http.Request) { + p.lock.Lock() + defer p.lock.Unlock() + log.Println(r.URL.String()) + rpt, err := p.makeReport() + if err != nil { + log.Printf("error: %v", err) + http.Error(w, err.Error(), http.StatusInternalServerError) + return + } + raw, err := json.Marshal(*rpt) + if err != nil { + log.Printf("error: %v", err) + http.Error(w, err.Error(), http.StatusInternalServerError) + return + } + w.WriteHeader(http.StatusOK) + w.Write(raw) +} + +``` - **See Also** +**See Also** * [Building Scope](/site/building.md)