mirror of https://github.com/istio/istio.io.git
114 lines
4.3 KiB
Markdown
114 lines
4.3 KiB
Markdown
---
|
|
title: Overview
|
|
description: Overview of distributed tracing in Istio.
|
|
weight: 1
|
|
keywords: [telemetry,tracing]
|
|
---
|
|
|
|
Distributed tracing enables users to track a request through mesh that is distributed across multiple services.
|
|
This allows a deeper understanding about request latency, serialization and parallelism via visualization.
|
|
|
|
Istio leverages [Envoy's distributed tracing](https://www.envoyproxy.io/docs/envoy/v1.10.0/intro/arch_overview/tracing) feature
|
|
to provide tracing integration out of the box. Specifically, Istio provides options to install various tracing backend
|
|
and configure proxies to send trace spans to them automatically.
|
|
See [Zipkin](../zipkin/), [Jaeger](../jaeger/) and [LightStep](/docs/tasks/telemetry/distributed-tracing/lightstep/) task docs about how Istio works with those tracing systems.
|
|
|
|
## Trace context propagation
|
|
|
|
Although Istio proxies are able to automatically send spans, they need some hints to tie together the entire trace.
|
|
Applications need to propagate the appropriate HTTP headers so that when the proxies send span information,
|
|
the spans can be correlated correctly into a single trace.
|
|
|
|
To do this, an application needs to collect and propagate the following headers from the incoming request to any outgoing requests:
|
|
|
|
* `x-request-id`
|
|
* `x-b3-traceid`
|
|
* `x-b3-spanid`
|
|
* `x-b3-parentspanid`
|
|
* `x-b3-sampled`
|
|
* `x-b3-flags`
|
|
* `x-ot-span-context`
|
|
|
|
If you look at the sample Python `productpage` service, for example,
|
|
you see that the application extracts the required headers from an HTTP request
|
|
using [OpenTracing](https://opentracing.io/) libraries:
|
|
|
|
{{< text python >}}
|
|
def getForwardHeaders(request):
|
|
headers = {}
|
|
|
|
# x-b3-*** headers can be populated using the opentracing span
|
|
span = get_current_span()
|
|
carrier = {}
|
|
tracer.inject(
|
|
span_context=span.context,
|
|
format=Format.HTTP_HEADERS,
|
|
carrier=carrier)
|
|
|
|
headers.update(carrier)
|
|
|
|
# ...
|
|
|
|
incoming_headers = ['x-request-id']
|
|
|
|
# ...
|
|
|
|
for ihdr in incoming_headers:
|
|
val = request.headers.get(ihdr)
|
|
if val is not None:
|
|
headers[ihdr] = val
|
|
|
|
return headers
|
|
{{< /text >}}
|
|
|
|
The reviews application (Java) does something similar:
|
|
|
|
{{< text java >}}
|
|
@GET
|
|
@Path("/reviews/{productId}")
|
|
public Response bookReviewsById(@PathParam("productId") int productId,
|
|
@HeaderParam("end-user") String user,
|
|
@HeaderParam("x-request-id") String xreq,
|
|
@HeaderParam("x-b3-traceid") String xtraceid,
|
|
@HeaderParam("x-b3-spanid") String xspanid,
|
|
@HeaderParam("x-b3-parentspanid") String xparentspanid,
|
|
@HeaderParam("x-b3-sampled") String xsampled,
|
|
@HeaderParam("x-b3-flags") String xflags,
|
|
@HeaderParam("x-ot-span-context") String xotspan) {
|
|
|
|
if (ratings_enabled) {
|
|
JsonObject ratingsResponse = getRatings(Integer.toString(productId), user, xreq, xtraceid, xspanid, xparentspanid, xsampled, xflags, xotspan);
|
|
{{< /text >}}
|
|
|
|
When you make downstream calls in your applications, make sure to include these headers.
|
|
|
|
## Trace sampling
|
|
|
|
Istio captures a trace for all requests by default when installing with the demo profile.
|
|
For example, when using the Bookinfo sample application above, every time you access
|
|
`/productpage` you see a corresponding trace in the
|
|
dashboard. This sampling rate is suitable for a test or low traffic
|
|
mesh. For a high traffic mesh you can lower the trace sampling
|
|
percentage in one of two ways:
|
|
|
|
* During the mesh setup, use the Helm option `pilot.traceSampling` to
|
|
set the percentage of trace sampling. See the
|
|
[Helm Install](/docs/setup/kubernetes/install/helm/) documentation for
|
|
details on setting options.
|
|
* In a running mesh, edit the `istio-pilot` deployment and
|
|
change the environment variable with the following steps:
|
|
|
|
1. To open your text editor with the deployment configuration file
|
|
loaded, run the following command:
|
|
|
|
{{< text bash >}}
|
|
$ kubectl -n istio-system edit deploy istio-pilot
|
|
{{< /text >}}
|
|
|
|
1. Find the `PILOT_TRACE_SAMPLING` environment variable, and change
|
|
the `value:` to your desired percentage.
|
|
|
|
In both cases, valid values are from 0.0 to 100.0 with a precision of 0.01.
|
|
|
|
|