[OpenTracing Go](https://github.com/opentracing/opentracing-go) Tracer for Jaeger (https://jaegertracing.io).
**IMPORTANT**: The library's import path is based on its original location under `github.com/uber`. Do not try to import it as `github.com/jaegertracing`, it will not compile. We might revisit this in the next major release.
We recommended using a dependency manager like [dep](https://golang.github.io/dep/)
and [semantic versioning](http://semver.org/) when including this library into an application.
For example, Jaeger backend imports this library like this:
```toml
[[constraint]]
name = "github.com/uber/jaeger-client-go"
version = "2.17"
```
If you instead want to use the latest version in `master`, you can pull it via `go get`.
Note that during `go get` you may see build errors due to incompatible dependencies, which is why
we recommend using semantic versions for dependencies. The error may be fixed by running
`make install` (it will install `dep` if you don't have it):
```shell
go get -u github.com/uber/jaeger-client-go/
cd $GOPATH/src/github.com/uber/jaeger-client-go/
git submodule update --init --recursive
make install
```
## Initialization
See tracer initialization examples in [godoc](https://godoc.org/github.com/uber/jaeger-client-go/config#pkg-examples)
and [config/example_test.go](./config/example_test.go).
### Environment variables
The tracer can be initialized with values coming from environment variables. None of the env vars are required
and all of them can be overridden via direct setting of the property on the configuration object.
Property| Description
--- | ---
JAEGER_SERVICE_NAME | The service name
JAEGER_AGENT_HOST | The hostname for communicating with agent via UDP
JAEGER_AGENT_PORT | The port for communicating with agent via UDP
JAEGER_ENDPOINT | The HTTP endpoint for sending spans directly to a collector, i.e. http://jaeger-collector:14268/api/traces
JAEGER_USER | Username to send as part of "Basic" authentication to the collector endpoint
JAEGER_PASSWORD | Password to send as part of "Basic" authentication to the collector endpoint
JAEGER_REPORTER_LOG_SPANS | Whether the reporter should also log the spans
JAEGER_REPORTER_MAX_QUEUE_SIZE | The reporter's maximum queue size
JAEGER_REPORTER_FLUSH_INTERVAL | The reporter's flush interval, with units, e.g. "500ms" or "2s" ([valid units][timeunits])
JAEGER_SAMPLER_TYPE | The sampler type
JAEGER_SAMPLER_PARAM | The sampler parameter (number)
JAEGER_SAMPLER_MANAGER_HOST_PORT | The HTTP endpoint when using the remote sampler, i.e. http://jaeger-agent:5778/sampling
JAEGER_SAMPLER_MAX_OPERATIONS | The maximum number of operations that the sampler will keep track of
JAEGER_SAMPLER_REFRESH_INTERVAL | How often the remotely controlled sampler will poll jaeger-agent for the appropriate sampling strategy, with units, e.g. "1m" or "30s" ([valid units][timeunits])
JAEGER_TAGS | A comma separated list of `name = value` tracer level tags, which get added to all reported spans. The value can also refer to an environment variable using the format `${envVarName:default}`, where the `:default` is optional, and identifies a value to be used if the environment variable cannot be found
JAEGER_DISABLED | Whether the tracer is disabled or not. If true, the default `opentracing.NoopTracer` is used.
JAEGER_RPC_METRICS | Whether to store RPC metrics
By default, the client sends traces via UDP to the agent at `localhost:6831`. Use `JAEGER_AGENT_HOST` and
`JAEGER_AGENT_PORT` to send UDP traces to a different `host:port`. If `JAEGER_ENDPOINT` is set, the client sends traces
to the endpoint via `HTTP`, making the `JAEGER_AGENT_HOST` and `JAEGER_AGENT_PORT` unused. If `JAEGER_ENDPOINT` is
secured, HTTP basic authentication can be performed by setting the `JAEGER_USER` and `JAEGER_PASSWORD` environment
variables.
### Closing the tracer via `io.Closer`
The constructor function for Jaeger Tracer returns the tracer itself and an `io.Closer` instance.
It is recommended to structure your `main()` so that it calls the `Close()` function on the closer
before exiting, e.g.
```go
tracer, closer, err := cfg.NewTracer(...)
defer closer.Close()
```
This is especially useful for command-line tools that enable tracing, as well as
for the long-running apps that support graceful shutdown. For example, if your deployment
system sends SIGTERM instead of killing the process and you trap that signal to do a graceful
