Part III: OTEL sidecar extension on Azure App Service for Linux - Language cheat-sheet

Microsoft

Nov 13, 2025

Building on Part II (and Part I), here’s a concise matrix for PHP, Python, Node.js, and .NET, plus the key app settings and quick troubleshooting steps.

Lang doc	OTEL libraries	AppSettings	Startup command example	Sample repo
PHP	Composer autoloader (vendor/autoload.php); PECL ext opentelemetry via php.ini (extension=opentelemetry.so); Composer plugins (e.g., Slim, PSR-18).	Main: OTEL_PHP_AUTOLOAD_ENABLED=true, SCM_DO_BUILD_DURING_DEPLOYMENT=true, OTEL_EXPORTER_OTLP_ENDPOINT=http://127.0.0.1:4318 Sidecar: map OTEL_PHP_AUTOLOAD_ENABLED	cp /home/site/wwwroot/default /etc/nginx/sites-enabled/default && nginx -s reload && bash /home/site/wwwroot/startup.sh (startup.sh: pecl install opentelemetry; add extension=opentelemetry.so; php-fpm)	PHP Sample
Python	Via opentelemetry-instrument wrapper; auto-patches Flask/requests; installed with pip; run app through opentelemetry-instrument.	Main: OTEL_TRACES_EXPORTER=otlp, OTEL_METRICS_EXPORTER=otlp, OTEL_LOGS_EXPORTER=otlp, OTEL_PYTHON_LOGGING_AAUTO_INSTRUMENTATION_ENABLED =true, SCM_DO_BUILD_DURING_DEPLOYMENT=true Sidecar: map OTEL_PYTHON_LOGGING_AUTO_INSTRUMENTATION_ENABLED	bash startup.sh (wait for pip install -r requirements.txt; then exec opentelemetry-instrument --traces_exporter otlp --metrics_exporter otlp flask run --host=0.0.0.0 --port=8000)	Python Sample
Node	npm: @opentelemetry/sdk-node, @opentelemetry/auto-instrumentations-node, @opentelemetry/exporter-trace-otlp-http; init in tracing.js; preload via --require or NODE_OPTIONS.	Main: OTEL_TRACES_EXPORTER=otlp, OTEL_METRICS_EXPORTER=otlp, OTEL_LOGS_EXPORTER=otlp, SCM_DO_BUILD_DURING_DEPLOYMENT=true	node --require ./tracing.js <your-app>.js (or set NODE_OPTIONS=--require ./tracing.js and use normal start)	Node Sample
Dotnet	NuGet packages (OpenTelemetry.Extensions.Hosting, OpenTelemetry.Instrumentation .AspNetCore, OpenTelemetry.Instrumentation.Http, OpenTelemetry.Exporter .OpenTelemetryProtocol); configure in Program.cs via AddOpenTelemetry() (ASP.NET Core + HttpClient).	Main: OTEL_DOTNET_AUTO_TRACES_ENABLED=true, OTEL_DOTNET_AUTO_METRICS_ENABLED=true, OTEL_DOTNET_AUTO_LOGS_ENABLED=true	No custom startup command needed	.NET Sample

Common App Settings added by default

Azure Monitor (Application Insights)

APPLICATIONINSIGHTS_CONNECTION_STRING = <your-application-insights-connection-string>
OTEL_EXPORTER = azuremonitor
OTEL_EXPORTER_OTLP_ENDPOINT = http://127.0.0.1:4318
OTEL_SERVICE_NAME = <your-app-name>

Elastic APM

ELASTIC_APM_ENDPOINT = https://<your-elastic-endpoint>
ELASTIC_APM_SECRET_TOKEN = <your-elastic-token>
OTEL_EXPORTER = elastic
OTEL_EXPORTER_OTLP_ENDPOINT = http://127.0.0.1:4318
OTEL_SERVICE_NAME = <your-app-name>

Notes:

These live on the main app; the sidecar extension reads what it needs and forwards data to the chosen backend.
Keep :4318 for OTLP/HTTP (default). Use :4317 only if you switch to OTLP/gRPC across your stack.
Set a meaningful OTEL_SERVICE_NAME (e.g., myapp-api) to make traces easy to find.

Sample repo (code & containers)

We’ve published a repo with working samples for PHP, Node.js, Python, and .NET showing both code-based and container-based setups using the OTEL sidecar extensions. Use it as your starting point: https://github.com/Azure-Samples/sidecar-samples/tree/main/otel-sidecar

Troubleshooting

No telemetry appearing

Sidecar status: Deployment Center → Containers → confirm the sidecar shows Running.
Settings check: Environment variables → confirm
OTEL_EXPORTER_OTLP_ENDPOINT=http://127.0.0.1:4318 and your backend creds (e.g., APPLICATIONINSIGHTS_CONNECTION_STRING or ELASTIC_APM_ENDPOINT/ELASTIC_APM_SECRET_TOKEN).
Logs: Monitoring → Log stream → view the sidecar container logs for errors or “Successfully exported” messages.
Debug logs: Add OTEL_TELEMETRY_LOG_LEVEL=debug in App settings, Apply, then re-check Log stream.

Sidecar fails to start

Requirements: Confirm your plan has sufficient resources (e.g., P0v3 or higher).
Required settings present:

Azure Monitor: APPLICATIONINSIGHTS_CONNECTION_STRING
Elastic: ELASTIC_APM_ENDPOINT, ELASTIC_APM_SECRET_TOKEN

Startup errors: Monitoring → Log stream → check sidecar startup logs for config issues.

High memory usage

Reduce volume: Enable sampling, filter health checks/noisy endpoints, lower log verbosity.
Scale up: Settings → Scale up (App Service plan) → choose a higher tier.

Conclusion & resources

With the OpenTelemetry sidecar extensions for Azure Monitor and Elastic APM, App Service for Linux makes end-to-end observability a drop-in add-on for both code and container apps. Grab the sample repo, wire up your connection string or token, and give it a try.