Appdash allows you to trace the end-to-end handling of requests and operations in your application (for perf and debugging). It displays timings and application-specific metadata for each step, and it displays a tree and timeline for each request and its children.
To use appdash, you must instrument your application with calls to an appdash recorder. You can record any type of event or operation. Recorders and schemas for HTTP (client and server) and SQL are provided, and you can write your own.
To install appdash, run:
go get -u sourcegraph.com/sourcegraph/appdash/cmd/...
A standalone example using Negroni and Gorilla packages is available in the
A demo / pure
net/http application (which is slightly more verbose) is also available at
cmd/appdash/example_app.go, and it can be ran easily using
appdash demo on the command line.
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Appdash uses vfsgen to package HTML templates with the appdash binary for
distribution. This means that if you want to modify the template data in
traceapp/tmpl you can first build using the
dev build tag, which makes the template data be reloaded from disk live.
After you're finished making changes to the templates, always run
go generate sourcegraph.com/sourcegraph/appdash/traceapp/tmpl so that the
data_vfsdata.go file is updated for normal Appdash users that aren't interested in modifying the template data.
Appdash follows the design and naming conventions of Google's Dapper. You should read that paper if you are curious about why certain architectural choices were made.
There are 4 main components/concepts in appdash:
- Spans: A span refers to an operation and all of its children. For example, an HTTP handler handles a request by calling other components in your system, which in turn make various API and DB calls. The HTTP handler's span includes all downstream operations and their descendents; likewise, each downstream operation is its own span and has its own descendents. In this way, appdash constructs a tree of all of the operations that occur during the handling of the HTTP request.
- Event: Your application records the various operations it performs (in the course of handling a request) as Events. Events can be arbitrary messages or metadata, or they can be structured event types defined by a Go type (such as an HTTP ServerEvent or an SQLEvent).
- Recorder: Your application uses a Recorder to send events to a Collector (see below). Each Recorder is associated with a particular span in the tree of operations that are handling a particular request, and all events sent via a Recorder are automatically associated with that context.
- Collector: A Collector receives Annotations (which are the encoded form of Events) sent by a Recorder. Typically, your application's Recorder talks to a local Collector (created with NewRemoteCollector. This local Collector forwards data to a remote appdash server (created with NewServer that combines traces from all of the services that compose your application. The appdash server in turn runs a Collector that listens on the network for this data, and it then stores what it receives.
Appdash has clients available for Go, Python (see
python/ subdir) and Ruby (see https://github.com/bsm/appdash-rb).
appdash was influenced by, and uses code from, Coda Hale's lunk.