This document is for a development version of Ceph.
JAEGER- DISTRIBUTED TRACING¶
Jaeger + Opentracing provides ready to use tracing services for distributed systems and is becoming the widely used standard because of their simplicity and standardization.
We use a modified jaeger-cpp-client the backend provided to the Opentracing API, which is responsible for the collection of spans, these spans are made with the use of smart pointers that carry the timestamp, TraceID and other meta info like a specific tag/log associated with the span to uniquely identify it across the distributed system.
BASIC ARCHITECTURE AND TERMINOLOGY¶
TRACE: A trace shows the data/execution path through a system.
SPAN: A single unit of a trace, it is a data structure that stores information like operation name, timestamps, ordering in a trace.
JAEGER CLIENT: language-specific implementations of the OpenTracing API.
JAEGER AGENT: a daemon that listens for spans sent over User Datagram Protocol. The agent is meant to be placed on the same host as the instrumented application. (acts like a sidecar listener)
JAEGER COLLECTOR: Jaeger agent sends the spans to this daemon which then stitches the spans together to form a trace(if enabled, also persists a database for these traces)
HOW TO GET STARTED USING TRACING?¶
Enabling jaegertracing with Ceph needs deployment Jaeger daemons + compiling Ceph with Jaeger, orchestrated to be used in vstart cluster for developers, this uses a jaeger all-in-one docker which isn’t recommended for production, but for testing purposes. Let’s look at all the steps needed:
Update system with Jaeger dependencies, using install-deps:$ WITH_JAEGER=true ./install-deps.sh
Compile Ceph with Jaeger enabled:
for precompiled build:$ cd build $ cmake -DWITH_JAEGER=ON ..
for fresh compilation using do_cmake.sh:$ ./do_cmake.sh -DWITH_JAEGER=ON && ninja vstart
3. After successful compiling, start a vstart cluster with –jaeger which will deploy jaeger all-in-one using container deployment services(docker/podman):$ MON=1 MGR=0 OSD=1 ../src/vstart.sh --with-jaeger
if the deployment is unsuccessful, you can deploy all-in-one service manually and start vstart cluster without jaeger as well.
Test the traces using rados-bench write:$ bin/rados -p test bench 5 write --no-cleanup