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zipkin-reporter-java

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Shared library for reporting zipkin spans on transports such as http or kafka

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# zipkin-reporter-java

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Zipkin Reporter buffers and sends trace data collected from tracer libraries to a Zipkin compatible backend.

This repository includes a Java reporting library with transport-specific senders.
Transport options include HTTP, Apache ActiveMQ, Apache Kafka, gRPC, RabbitMQ, Scribe (Apache Thrift)
and Apache Pulsar. Requires JRE 6 or later.

# Usage
These components can be called when spans have been recorded and ready to send to zipkin.

## Encoder
The span encoder is a specialized form of Zipkin's Codec, which only deals with encoding one span.
It is also extensible in case the type of span reported is not `zipkin2.Span`

## Reporter
After recording an operation into a span, it needs to be reported out of process. There are two
builtin reporter implementations in this library, although you are free to create your own.

The simplest mechanism is printing out spans as they are reported.

```java
Reporter.CONSOLE.report(span);
```

## AsyncReporter
AsyncReporter is how you actually get spans to zipkin. By default, it waits up to a second
before flushes any pending spans out of process via a BytesMessageSender.

```java
reporter = AsyncReporter.create(URLConnectionSender.create("http://localhost:9411/api/v2/spans"));

// Schedules the span to be sent, and won't block the calling thread on I/O
reporter.report(span);
```

## Brave
Those using the [Brave library](https://github.com/openzipkin/brave) can skip
overhead by using `AsyncZipkinSpanHandler`.

Ex.
```java
sender = URLConnectionSender.create("http://localhost:9411/api/v2/spans");
zipkinSpanHandler = AsyncZipkinSpanHandler.create(sender); // don't forget to close!
tracingBuilder.addSpanHandler(zipkinSpanHandler);
```

See [zipkin-reporter-brave](brave/README.md) for more details.

## Spring Beans
If you are trying to trace legacy applications, you may be interested in
[Spring XML Configuration](spring-beans/). This allows you to trace legacy
Spring 2.5+ applications without any custom code.

### Tuning

By default AsyncReporter starts a thread to flush the queue of reported
spans. Spans are encoded before enqueuing so it is easiest to relate the
backlog as a function of bytes.

Here are the most important properties to understand when tuning.

| Property          | Description                                                                                                                               |
|-------------------|-------------------------------------------------------------------------------------------------------------------------------------------|
| `queuedMaxSpans`  | Maximum backlog of spans reported vs sent. Default 10000                                                                                  |
| `queuedMaxBytes`  | Maximum backlog of span bytes reported vs sent. Corresponds to `ReporterMetrics.updateQueuedBytes`. Disabled by default                   |
| `messageMaxBytes` | Maximum bytes sendable per message including overhead. Default `500,000` bytes (`500KB`). Defined by `BytesMessageSender.messageMaxBytes` |
| `messageTimeout`  | Maximum time to wait for messageMaxBytes to accumulate before sending. Default 1 second                                                   |
| `closeTimeout`    | Maximum time to block for in-flight spans to send on close. Default 1 second                                                              |

#### Dealing with span backlog
When `messageTimeout` is non-zero, a single thread is responsible for
bundling spans into a message for the sender. If you are using a blocking
sender, a surge of reporting activity could lead to a queue backup. This
will show in metrics as spans dropped. If you get into this position,
switch to an asynchronous sender (like kafka), or increase the concurrency
of your sender.

Spikes of high CPU could be due to encoding many spans, caused indirectly
by a large `messageTimeout` or `messageMaxBytes`. Consider lowering the
`messageMaxBytes` if this occurs, as it will result in less work per
message.

## BytesMessageSender
The sender component handles the last step of sending a list of encoded spans onto a transport.
This involves I/O, so you can call `sender.send(Collections.emptyList())` to check it works before
using.

BytesMessageSender is used by AsyncReporter, but you can also create your own if you need to.
```java
class CustomReporter implements Flushable {

--snip--
  URLConnectionSender sender = URLConnectionSender.json("http://localhost:9411/api/v2/spans");

Callback callback = new IncrementSpanMetricsCallback(metrics);

// Is the connection healthy?
  public boolean ok() {
    try {
      sender.send(Collections.emptyList());
      return true;
    } catch (Exception e) {
      return false;
    }
  }

public void report(Span span) {
    pending.add(SpanBytesEncoder.JSON_V2.encode(span));
  }

@Override
  public void flush() throws IOException {
    if (pending.isEmpty()) return;
    List<byte[]> drained = new ArrayList<byte[]>(pending.size());
    pending.drainTo(drained);
    if (drained.isEmpty()) return;

sender.send(drained);
  }
```

### Protocol Buffers Encoding
By default, senders use json v2 encoding, which is easy to understand, but
twice as large as binary encoding for normal spans. If you are running a
recent (2.8+) version of Zipkin server, consider [Protocol Buffers](https://developers.google.com/protocol-buffers/docs/proto3)
when you want to optimize for least size.

You can switch to proto3 encoding like so:

```java
sender = KafkaSender.newBuilder()
                    .encoding(Encoding.PROTO3)
                    .bootstrapServers("192.168.99.100:9092")
                    .build()
```

### Legacy Encoding
By default, senders use json v2 encoding, which is easy to understand and
twice as efficient as the v1 json encoding. However, it relies on recent
(1.31+) versions of zipkin server.

You can switch to v1 encoding like so:

```java
reporter = AsyncReporter.builder(URLConnectionSender.create("http://localhost:9411/api/v1/spans"))
                        .build(SpanBytesEncoder.JSON_V1);
```

## Artifacts
All artifacts publish to the group ID "io.zipkin.zipkin.reporter2". We use a common
release version for all components.

### Library Releases
Releases are at [Maven Central](https://central.sonatype.com/search?q=zipkin-reporter&namespace=io.zipkin.reporter2)

### Library Snapshots
Snapshots are uploaded to [Sonatype](https://central.sonatype.com/repository/maven-snapshots/) after
commits to master.

### Version alignments
When using multiple reporter components, you'll want to align versions
in one place. This allows you to more safely upgrade, with less worry
about conflicts.

You can use our Maven instrumentation BOM (Bill of Materials) for this:

Ex. in your dependencies section, import the BOM like this:
```xml
  <dependencyManagement>
    <dependencies>
      <dependency>
        <groupId>io.zipkin.reporter2</groupId>
        <artifactId>zipkin-reporter-bom</artifactId>
        <version>${zipkin-reporter.version}</version>
        <type>pom</type>
        <scope>import</scope>
      </dependency>
    </dependencies>
  </dependencyManagement>
```

Now, you can leave off the version when choosing any supported
instrumentation. Also, any indirect use will have versions aligned:
```xml
<dependency>
  <groupId>io.zipkin.reporter2</groupId>
  <artifactId>zipkin-sender-okhttp3</artifactId>
</dependency>
```

With this in place, you can use the property `zipkin-reporter.version` to override dependency
versions coherently. This is most commonly to test a new feature or fix.

Note: If you override a version, always double check that your version
is valid (equal to or later) than what you are updating. This will avoid
class conflicts.

zipkin-reporter-java

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