b3-propagation
opentelemetry-specificatio
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b3-propagation
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OpenTelemetry in 2023
I've been playing with OTEL for a while, with a few backends like Jaeger and Zipkin, and am trying to figure out a way to perform end to end timing measurements across a graph of services triggered by any of several events.
Consider this scenario: There is a collection of services that talk to one another, and not all use HTTP. Say agent A0 makes a connection to agent A1, this is observed by service S0 which triggers service S1 to make calls to S2 and S3, which propagate elsewhere and return answers.
If we limit the scope of this problem to services explicitly making HTTP calls to other services, we can easily use the Propagators API [1] and use X-B3 headers [2] to propagate the trace context (trace ID, span ID, parent span ID) across this graph, from the origin through to the destination and back. This allows me to query the metrics collector (Jaeger or Zipkin) using this trace ID, look at the timestamps originating at the various services and do a T_end - T_start to determine the overall time taken by one call for a round trip across all the related services.
However, this breaks when a subset of these functions cannot propagate the B3 trace IDs for various reasons (e.g., a service is watching a specific state and acts when the state changes). I've been looking into OTEL and other related non-OTEL ways to capture metrics, but it appears there's not much research into this area though it does not seem like a unique or new problem.
Has anyone here looked at this scenario, and have you had any luck with OTEL or other mechanisms to get results?
[1] https://opentelemetry.io/docs/specs/otel/context/api-propaga...
[2] https://github.com/openzipkin/b3-propagation
[3] https://www.w3.org/TR/trace-context/
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OpenTelemetry and Istio: Everything you need to know
(Note that OpenTelemetry uses, by default, the W3C context propagation specification, while Istio uses the B3 context propagation specification โ this can be modified).
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Spring Cloud Sleuth in action
The default format for context propagation is B3 so we use headers X-B3-TraceId and X-B3-SpanId
opentelemetry-specificatio
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Migrating to OpenTelemetry
Sure, happy to provide more specifics!
Our main issue was the lack of a synchronous gauge. The officially supported asynchronous API of registering a callback function to report a gauge metric is very different from how we were doing things before, and would have required lots of refactoring of our code. Instead, we wrote a wrapper that exposes a synchronous-like API: https://gist.github.com/yolken-airplane/027867b753840f7d15d6....
It seems like this is a common feature request across many of the SDKs, and it's in the process of being fixed in some of them (https://github.com/open-telemetry/opentelemetry-specificatio...)? I'm not sure what the plans are for the golang SDK specifically.
Another, more minor issue, is the lack of support for "constant" attributes that are applied to all metrics. We use these to identify the app, among other use cases, so we added wrappers around the various "Add", "Record", "Observe", etc. calls that automatically add these. (It's totally possible that this is supported and I missed it, in which case please let me know!).
Overall, the SDK was generally well-written and well-documented, we just needed some extra work to make the interfaces more similar to the ones were were using before.
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OpenTelemetry in 2023
Two problems with OpenTelemetry:
1. It doesn't know what the hell it is. Is it a semantic standard? Is a protocol? It is a facade? What layer of abstraction does it provide? Answer: All of the above! All the things! All the layers!
2. No one from OpenTelemetry has actually tried instrumenting a library. And if they have, they haven't the first suggestion on how instrumenters should actually use metrics, traces, and logs. Do you write to all three? To one? I asked this question two years ago, not a single response. [1]
[1] https://github.com/open-telemetry/opentelemetry-specificatio...
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Go standard library: structured, leveled logging
That's why you have otel logging: https://github.com/open-telemetry/opentelemetry-specificatio...
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Monarch: Googleโs Planet-Scale In-Memory Time Series Database
There are a large amount of subtle tradeoffs around the bucketing scheme (log, vs. log-linear, base) and memory layout (sparse, dense, chunked) the amount of configurability in the histogram space (circllhist, DDSketch, HDRHistogram, ...). A good overview is this discussion here:
https://github.com/open-telemetry/opentelemetry-specificatio...
As for the circllhist: There are no knobs to turn. It uses base 10 and two decimal digits of precision. In the last 8 years I have not seen a single use-case in the operational domain where this was not appropriate.
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OpenTelemetry
A good place to look at is the milestones on GitHub: https://github.com/open-telemetry/opentelemetry-specificatio...
Logging is still experimental in the spec. Metrics API is feature freeze and the protocol is stable, so it's more on language SDKs to stabilize their implementations. This is a focus for several of them right now.
What are some alternatives?
trace-context-w3c - W3C Trace Context purpose of and what kind of problem it came to solve.
skywalking - APM, Application Performance Monitoring System
zipkin - Zipkin is a distributed tracing system
SLF4J - Simple Logging Facade for Java
spring-cloud-sleuth-in-action - ๐ Spring Cloud Sleuth in Action
opentelemetry-specification - Specifications for OpenTelemetry
odigos - Distributed tracing without code changes. ๐ Instantly monitor any application using OpenTelemetry and eBPF
semantic-conventions - Defines standards for generating consistent, accessible telemetry across a variety of domains
community - OpenTelemetry community content
jvm-serializers - Benchmark comparing serialization libraries on the JVM
oteps - OpenTelemetry Enhancement Proposals
zipkin-api - Zipkin's language independent model and HTTP Api Definitions