Add observability: real OTLP metrics/traces to grafana/otel-lgtm, Docker Compose auto-wiring, and a dual-version (Boot 4.0 vs 4.1) proof of the new OTEL_* env var support
Companion module for the rewritten ankurm.com Prometheus/Grafana monitoring post. Verified against a real running grafana/otel-lgtm container (not mocked): 8 real requests produce a real orders_placed_total metric queried back from the bundled Prometheus-compatible API with zero management.otlp.* properties, auto-wired entirely by Boot's Docker Compose service-connection detection. Two real findings surfaced along the way and documented rather than smoothed over: @Observed silently produces no span without an explicit ObservedAspect bean (AspectJ weaving alone is not sufficient, despite Micrometer Tracing being active), and OTEL_EXPORTER_OTLP_ENDPOINT already worked on Boot 4.0 via Micrometer's own OtlpConfig fallback -- what's actually new in 4.1 is the rest of the standard OTEL_* surface (verified with OTEL_METRIC_EXPORT_INTERVAL against identical source compiled on both Boot 4.0.8 and 4.1.1). Also fixes the root README's module table, which was missing a row for resilience4j-circuit-breaker (added in a previous commit but never indexed here).
This commit is contained in:
Claude
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# env-var-proof
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Answers one factual question with real execution instead of quoting a changelog: does Spring
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Boot 4.1 actually honor standard `OTEL_*` environment variables that Boot 4.0 did not?
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`boot40/` and `boot41/` contain the **identical** `OtelEnvProofApplication.java` -- the only
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difference between the two Maven modules is the `spring-boot-starter-parent` version (4.0.8 vs
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4.1.1). Both start with only `OTEL_EXPORTER_OTLP_ENDPOINT` and `OTEL_METRIC_EXPORT_INTERVAL` set
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(no `management.otlp.*` Spring properties anywhere) and point at `stub-receiver/`, a
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dependency-free stand-in for an OTLP collector that just logs every POST it receives.
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See [`../docs/output/04-otel-env-vars-4.0-vs-4.1.txt`](../docs/output/04-otel-env-vars-4.0-vs-4.1.txt)
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for the captured result, and [`../docs/03-otel-env-vars.md`](../docs/03-otel-env-vars.md) for the
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write-up. Run it yourself with [`../scripts/run-env-var-proof.sh`](../scripts/run-env-var-proof.sh).
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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<parent>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-parent</artifactId>
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<version>4.0.8</version>
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<relativePath/>
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</parent>
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<groupId>com.ankurm</groupId>
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<artifactId>otel-env-proof-40</artifactId>
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<version>1.0.0</version>
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<properties>
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<java.version>25</java.version>
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</properties>
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<dependencies>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter</artifactId>
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</dependency>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-actuator</artifactId>
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</dependency>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-opentelemetry</artifactId>
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</dependency>
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</dependencies>
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<build>
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<plugins>
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<plugin>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-maven-plugin</artifactId>
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</plugin>
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</plugins>
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</build>
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</project>
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+37
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package com.ankurm.otelproof;
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import io.micrometer.core.instrument.Counter;
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import io.micrometer.core.instrument.MeterRegistry;
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import org.springframework.boot.CommandLineRunner;
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import org.springframework.boot.SpringApplication;
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import org.springframework.boot.autoconfigure.SpringBootApplication;
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import org.springframework.context.annotation.Bean;
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/**
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* Sets ONLY standard OTEL_* environment variables (no management.otlp.* Spring properties at
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* all) and checks whether metrics actually reach the configured OTLP endpoint within a fixed
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* observation window. Identical source file used against Boot 4.0.8 and Boot 4.1.1 -- only the
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* parent POM version differs between the two modules that compile this file.
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*/
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@SpringBootApplication
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public class OtelEnvProofApplication {
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public static void main(String[] args) throws InterruptedException {
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var ctx = SpringApplication.run(OtelEnvProofApplication.class, args);
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MeterRegistry registry = ctx.getBean(MeterRegistry.class);
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Counter counter = Counter.builder("otel.env.proof.calls").register(registry);
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long start = System.currentTimeMillis();
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long windowMs = 20_000;
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while (System.currentTimeMillis() - start < windowMs) {
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counter.increment();
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Thread.sleep(200);
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}
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System.out.println("otel.env.proof.calls final count = " + counter.count());
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System.exit(0);
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}
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@Bean
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CommandLineRunner logStart() {
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return args -> System.out.println("otel-env-proof app started, MeterRegistry bean present");
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}
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}
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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<parent>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-parent</artifactId>
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<version>4.1.1</version>
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<relativePath/>
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</parent>
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<groupId>com.ankurm</groupId>
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<artifactId>otel-env-proof-41</artifactId>
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<version>1.0.0</version>
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<properties>
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<java.version>25</java.version>
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</properties>
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<dependencies>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter</artifactId>
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</dependency>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-actuator</artifactId>
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</dependency>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-opentelemetry</artifactId>
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</dependency>
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</dependencies>
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<build>
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<plugins>
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<plugin>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-maven-plugin</artifactId>
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</plugin>
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</plugins>
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</build>
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</project>
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+37
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package com.ankurm.otelproof;
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import io.micrometer.core.instrument.Counter;
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import io.micrometer.core.instrument.MeterRegistry;
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import org.springframework.boot.CommandLineRunner;
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import org.springframework.boot.SpringApplication;
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import org.springframework.boot.autoconfigure.SpringBootApplication;
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import org.springframework.context.annotation.Bean;
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/**
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* Sets ONLY standard OTEL_* environment variables (no management.otlp.* Spring properties at
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* all) and checks whether metrics actually reach the configured OTLP endpoint within a fixed
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* observation window. Identical source file used against Boot 4.0.8 and Boot 4.1.1 -- only the
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* parent POM version differs between the two modules that compile this file.
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*/
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@SpringBootApplication
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public class OtelEnvProofApplication {
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public static void main(String[] args) throws InterruptedException {
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var ctx = SpringApplication.run(OtelEnvProofApplication.class, args);
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MeterRegistry registry = ctx.getBean(MeterRegistry.class);
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Counter counter = Counter.builder("otel.env.proof.calls").register(registry);
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long start = System.currentTimeMillis();
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long windowMs = 20_000;
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while (System.currentTimeMillis() - start < windowMs) {
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counter.increment();
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Thread.sleep(200);
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}
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System.out.println("otel.env.proof.calls final count = " + counter.count());
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System.exit(0);
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}
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@Bean
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CommandLineRunner logStart() {
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return args -> System.out.println("otel-env-proof app started, MeterRegistry bean present");
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}
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}
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@@ -0,0 +1,43 @@
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import com.sun.net.httpserver.HttpServer;
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import java.io.OutputStream;
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import java.net.InetSocketAddress;
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import java.nio.file.Files;
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import java.nio.file.Path;
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import java.nio.file.StandardOpenOption;
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import java.time.Instant;
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/**
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* A minimal, dependency-free stand-in for an OTLP collector. It accepts any POST to any path,
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* logs the path, content-length and arrival time to a file (one line per request), and returns
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* 200 OK with an empty OTLP-shaped protobuf response body. Used only to answer one factual
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* question: did this JVM actually attempt to POST metrics to the configured OTLP endpoint within
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* the observation window? Not a real collector -- doesn't parse the protobuf payload.
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*
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* Usage: java StubOtlpReceiver.java <port> <logFile>
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*/
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public class StubOtlpReceiver {
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public static void main(String[] args) throws Exception {
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int port = Integer.parseInt(args[0]);
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Path logFile = Path.of(args[1]);
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Files.deleteIfExists(logFile);
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Files.createFile(logFile);
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HttpServer server = HttpServer.create(new InetSocketAddress("0.0.0.0", port), 0);
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server.createContext("/", exchange -> {
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String line = Instant.now() + " " + exchange.getRequestMethod() + " " + exchange.getRequestURI()
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+ " content-length=" + exchange.getRequestHeaders().getFirst("Content-Length") + System.lineSeparator();
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Files.writeString(logFile, line, StandardOpenOption.APPEND);
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exchange.getRequestBody().readAllBytes(); // drain
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byte[] resp = new byte[0];
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exchange.sendResponseHeaders(200, resp.length);
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try (OutputStream os = exchange.getResponseBody()) {
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os.write(resp);
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}
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});
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server.setExecutor(null);
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server.start();
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System.out.println("StubOtlpReceiver listening on :" + port + ", logging to " + logFile);
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// Run until killed externally.
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Thread.currentThread().join();
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}
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}
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