Skip to content
This repository has been archived by the owner on Apr 20, 2021. It is now read-only.

Commit

Permalink
docs/plugins: sync docs with changes site changes
Browse files Browse the repository at this point in the history 
This patch applies the same changes from the review of
weaveworks#2008
  • Loading branch information
Alessandro Puccetti committed Nov 14, 2016
1 parent 953548d commit 655e667
Showing 1 changed file with 65 additions and 62 deletions.
127 changes: 65 additions & 62 deletions examples/plugins/README.md
View file
Original file line number Diff line number Diff line change
Expand Up @@ -8,39 +8,40 @@ The list of the current running plugins is displayed next to the label `PLUGINS`

## Official Plugins

You can find all the official plugins at [Weaveworks Plugins](https://github.com/weaveworks-plugins).
Official Weave Scope plugins can be found at [Weaveworks Plugins](https://github.com/weaveworks-plugins).

* [IOWait](https://github.com/weaveworks-plugins/scope-iowait): a Go plugin using [iostat](https://en.wikipedia.org/wiki/Iostat) to provide host-level CPU IO wait or idle metrics.
* [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.

* [HTTP Statistics](https://github.com/weaveworks-plugins/scope-http-statistics): A Python plugin using [bcc](http://iovisor.github.io/bcc/) to track multiple metrics about HTTP per process, without any application-level instrumentation requirements and negligible performance toll. This plugin is a work in progress, as of now it implements two metrics (for more information read the [plugin documentation](https://github.com/weaveworks-plugins/scope-http-statistics)):
* [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 with a negligible performance toll. This plugin is a work in progress, and 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).

* [Traffic Control](https://github.com/weaveworks-plugins/scope-traffic-control): This plugin allows the user to modify latency and packet loss for a specific container via buttons in the UI's container detailed view.
* [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.

* [Volume Count](https://github.com/weaveworks-plugins/scope-volume-count): This plugin is a Python application that asks docker for the the number of mounted volumes for each container, providing container-level count.
* [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.

## Plugins Internals
## How Plugins Communicate with Scope
This section explains the fundamental parts of the plugins structure necessary to understand how a plugin communicates with Scope.
You can find more practical examples in [Weaveworks Plugins](https://github.com/weaveworks-plugins) repositories.

### Plugin ID
### Plugin IDs

Each plugin should have an unique ID. It is forbidden to change it
during the plugin's lifetime. The scope probe will get the plugin's ID
from the plugin's socket filename. For example, the socket named
`my-plugin.sock`, the scope probe will deduce the ID as
`my-plugin`. IDs can only contain alphanumeric sequences, optionally
separated with a dash.
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.

### Plugin registration
### Registering Plugins

All plugins should listen for HTTP connections on a unix socket in the
`/var/run/scope/plugins` directory. The scope probe will recursively
scan that directory every 5 seconds, to look for sockets being added
(or removed). It is also valid to put the plugin unix socket in a
sub-directory, in case you want to apply some permissions, or store
other information with the socket.
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.

### Protocol

Expand All @@ -57,9 +58,9 @@ Implementing this interface means listening for HTTP requests at `/report`.

#### Report

When the scope probe discovers a new plugin unix socket it will begin
When a scope probe discovers a new plugin UNIX socket it will begin
periodically making a `GET` request to the `/report` endpoint. The
report data structure returned from this will be merged into 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.

Expand All @@ -86,30 +87,30 @@ For example:
Note that the `Plugins` section includes exactly one plugin
description. The plugin description fields are:

* `id` is used to check for duplicate plugins. It is
* `id` - checks for duplicate plugins. It is
required. Described in [the Plugin ID section](#plugin-id).
* `label` is a human readable plugin label displayed in the UI. It is
* `label` - 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
* `description` - displayed in the UI.
* `interfaces` - a list of interfaces which this plugin supports. It
is required, and must contain at least `["reporter"]`.
* `api_version` is used to ensure both the plugin and the scope probe
* `api_version` - ensure both the plugin and the scope probe
can speak to each other. It is required, and must match the probe.

#### Controller interface

Plugins _may_ implement the controller interface. Implementing the
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 will receive them only
for controls it exposed in its reports. The requests will come to the
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 will have a JSON-encoded body with the following contents:
The `POST` requests contain a JSON-encoded body with the following contents:

```json
{
Expand All @@ -119,10 +120,10 @@ The `POST` requests will have a JSON-encoded body with the following contents:
}
```

The body of the response should also be a JSON-encoded data. Usually
the body would be an empty JSON object (so, "{}" after
serialization). If some error happens during handling the control,
then the plugin can send a response with an `error` field set, for
The body of the response should also be a JSON-encoded data. In most cases,
the body is an empty JSON object (so, "{}" after
serialization). If an error happens when handling the control,
then the plugin sends a response with an `error` field set, for
example:

```json
Expand All @@ -131,11 +132,11 @@ example:
}
```

Sometimes the control activation can make the control obsolete, so the
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 can send a shortcut report by filling the
`ShortcutReport` field in the response, like for example:
to work, the plugin sends a shortcut report by filling the
`ShortcutReport` field in the response, like so:

```json
{
Expand All @@ -145,11 +146,10 @@ to work, the plugin can send a shortcut report by filling the

##### How to expose controls

Each topology in the report (be it host, pod, endpoint and so on) has
a set of available controls a node in the topology may want to
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 having a
different control from the two:
two controls (`ctrl-one` and `ctrl-two`) and two nodes, each with a different control defined:

```json
{
Expand Down Expand Up @@ -194,8 +194,8 @@ different control from the two:
}
```

When control "ctrl-one" is activated, the plugin will receive a
request like:
When control "ctrl-one" is activated, the plugin receives a
request as follows:

```json
{
Expand All @@ -209,30 +209,31 @@ 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/)

##### Node naming
##### Naming Nodes

Very often the controller plugin wants to add some controls to already
existing nodes (like controls for network traffic management to nodes
Often the controller plugin may want to add some 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.

For containers, images, hosts and others the ID is usually formatted
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. There is a fixed
set of tags used by the probe:
hostname. The `${tag}` denotes the type of the node.

- host
- container
- container_image
- pod
- service
- deployment
- replica_set
There is a fixed set of tags used by the probe:

The examples of "tagged" node names:
- `host`
- `container`
- `container_image`
- `pod`
- `service`
- `deployment`
- `replica_set`

These are examples of "tagged" node names:

- The Docker container with full ID
2299a2ca59dfd821f367e689d5869c4e568272c2305701761888e1d79d7a6f51:
Expand All @@ -243,17 +244,19 @@ The examples of "tagged" node names:

The fixed set of tags listed above is not a complete set of names a
node can have though. For example, nodes representing processes are
have ID formatted as `${host};${pid}`. Probably the easiest ways to
have IDs formatted as `${host};${pid}`. The easiest way to
discover how the nodes are named are:

- Read the code in
1. Read the code in
[report/id.go](https://github.com/weaveworks/scope/blob/master/report/id.go).
- Browse the Weave Scope GUI, select some node and search for an `id`
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;<host>","label":"example.com","topologyId":"hosts"}],…`
URL, you can find the `example.com;<host>` which is an ID of the node
representing the host.
- Mentally substitute the `<SLASH>` with `/`. This can appear in
3. Mentally substitute the `<SLASH>` with `/`. This can appear in
Docker image names, so `docker.io/alpine` in the address bar will
be `docker.io<SLASH>alpine`.

For more detailed information visit [https://www.weave.works/documentation/scope-latest-plugins/](https://www.weave.works/documentation/scope-latest-plugins/)

0 comments on commit 655e667

Please sign in to comment.