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OpenTelemetry + Rust

Intro

This is a prototype PHP extension, using phper to expose opentelemetry-rust via PHP classes and implement auto-instrumentation.

The initial idea was to implement the PHP API in an extension, which could be a drop-in replacement for the core of opentelemetry-php. Since 3rd parties are strongly encouraged to only depend on the API, this should be all they need.

As it's slowly evolved and things have changed in the official opentelemetry-php implementation, the focus has shifted to being a small and fast opentelemetry implementation for legacy PHP versions that currently do not have an official way to use OpenTelemetry.

I've focussed development whilst thinking about a large legacy shared PHP host at my day job, where we have hundreds of small to medium PHP applications running on a single server (99% running as sub-directories in one Apache vhost), and we want to be able to trace them without modifying the code. There is a mix of frameworks, and some applications that pre-date modern frameworks.

Supported PHP versions

This works on all PHP versions supported by phper (7.0+). I've mostly tested against 8.4, 7.4 and some light testing against 7.0. Auto-instrumentation is implemented via the zend_observer API for PHP 8.0+, and via zend_execute_ex + zend_execute_internal for PHP 7.x.

PHP 7.x

Note that writing to stdout/stderr during MSHUTDOWN doesn't seem to work in PHP 7.x, so console exporting and log writing do not work for this stage. This mostly affects tests, and OTLP exporting works as expected.

Installation

All build approaches require llvm-dev, libclang-dev (at least 9.0), rust compiler and cargo.

PIE (PHP Installer for Extensions)

Only works for PHP versions supported by PIE (8.1+)

php pie.phar install brettmc/otel-php-rust:<version>

PECL

todo

Manual

Debugging

There's a bunch of logging from the extension and the underlying opentelemetry-rust and dependencies. It's configurable via .ini:

otel.log.level -> error (default), warn, info, debug or trace

otel.log.file -> /dev/stderr (default), or another file/location of your choosing

If you really want to see what's going on, set the log level to trace and you'll get a lot of logs.

In PHP 7.x, logging to stdout/stderr during MSHUTDOWN doesn't work, so you will need to set otel.log.file to a file location if you want to see logs from shutdown phase.

SAPI support

Tested against cli-server, apache2handler, cgi-fcgi and cli.

cli

Does not auto-create a root span by default, use .ini otel.cli.create_root_span to enable.

This should cover cli-based PHP runtimes (roadrunner, react, etc.), but has only been tested against RoadRunner.

Features

• Auto-instrumentation of userland and internal code
  • using either Zend Observer API (PHP 8.0+), or zend_execute_ex/zend_execute_internal (PHP 7.x)
• Start a span in RINIT, use traceparent headers, set HTTP response code in RSHUTDOWN
• TracerProvider created in RINIT (so that child processes have a working instance)
• Spans can be built through a SpanBuilder, some updates made (not all implemented yet), and end()ed
• Spans can be activate()d, and scope detached
• Spans export to stdout, otlp (grpc + http/protobuf)
• Batch and Simple span processors
• Get SpanContext from a Span
• Access "local root span"
• memory exporter for testing
• Support for shared hosting (ie one apache/fpm server with multiple sites), via .env files and otel.dotenv.per_request ini setting
• Disabling of auto-instrumentation via .ini setting otel.auto.disabled_plugins
  • eg otel.auto.disabled_plugins=laminas,psr18
• Configure OTEL_SERVICE_NAME, OTEL_RESOURCE_ATTRIBUTES and OTEL_DISABLED via .env (for multiple applications on the same host, you can override the general server environment variables)
• Some initial auto-instrumentation plugins:
  • Laminas
  • Zend Framework 1
  • PSR-18 HTTP client

Configuration

.ini

If either otel.env.set_from_server or otel.env.dotenv.enabled is set to true, the extension will back up the current environment variables on RINIT, and restore them on RSHUTDOWN.

Environment variables

All official OpenTelemetry SDK configuration environment variables understood by opentelemetry-rust.

If variables are not set in the process environment (eg via apache SetEnv), then set otel.env.set_from_server via php.ini, and OTEL_* variables from $_SERVER will be set in the environment.

.env files

OTEL_SERVICE_NAME, OTEL_RESOURCE_ATTRIBUTES and OTEL_SDK_DISABLED can be set in a .env file. Other variables should be set in the environment (todo: could be relaxed to allow setting all OpenTelemetry SDK configuration variables in the .env file).

Usage

Auto-instrumentation

By installing the extension and providing the basic SDK configuration that opentelemetry expects, each HTTP request will generate an HTTP server root span. There are some initial auto-instrumentation plugins for some legacy frameworks.

Manual instrumentation

Basic usage:

Some more advanced stuff:

Plugins

Mostly the framework plugins hook in to routing mechanism of that framework, update the root span's name to something more meaningful, and add some attributes.

A couple of non-standard attributes are added if the data is available: php.framework.name, php.framework.module.name, php.framework.controller.name, php.framework.action.name.

Laminas

Hooks Laminas\Mvc\MvcEvent::setRouteMatch. Sets framework name, and uses the RouteMatch to set module, controller and action names. Hooks some of the Laminas\Db methods to create CLIENT spans for database queries.

Zend Framework 1

Hooks Zend_Controller_Router_Interface::route. Sets framework name, and uses the Zend_Controller_Request_Abstract to set module, controller and action names.

Hooks some Zend_Db methods to create CLIENT spans for database queries.

Psr-18

Hooks Psr\Http\Client\ClientInterface::sendRequest, creates a CLIENT span and injects the traceparent header into outgoing HTTP requests.

Multi-site support

Vhosts

If providing configuration via Apache SetEnv directives, or FPM env[OTEL_*] variables, you should enable the otel.env.set_from_server setting in your php.ini, so that the extension will set the environment variables from the server environment on RINIT, and restore them on RSHUTDOWN.

For example (untested):

If you cannot modify vhost config, you can also use the .env file support described below.

No vhosts or multiple applications per vhost

If you have multiple sites on a single host (for example each application is a subdirectory of the web root), you can use the .env file support to set the environment variables for each site.

During request startup (RINIT), the extension will look for a .env file in the directory of the processed .php file (eg /var/www/site1/public/index.php -> /var/www/site1/public/.env), and traverse up until DOCUMENT_ROOT is reached. If a .env file is found, it will be checked for OTEL_SDK_DISABLED, OTEL_SERVICE_NAME and OTEL_RESOURCE_ATTRIBUTES variables, and if they are set, they will be set in the current environment, and the original values restored at RSHUTDOWN.

NB that the modified environment variables may not be reflected in $_SERVER, but should be visible via getenv().

Opt-in or opt-out

OpenTelemetry can be either opt-in, or opt-out, using environment variables and .env files.

If you want to disable OpenTelemetry by default, and enable it for specific applications, you can set OTEL_DISABLED=true in the server environment, and then set OTEL_DISABLED=false in the .env file for each application you want to enable observability for.

If you want to enable OpenTelemetry by default, and disable it for specific applications, you can set OTEL_DISABLED=false in the server environment, and then set OTEL_DISABLED=true in the .env file for each application you want to disable observability for.

What doesn't work or isn't implemented?

• Context storage - otel-rust doesn't support storing non-simple values, and context keys are created at compile time. This will probably never work like opentelemetry-php.
• It could use more interfaces to align with the official OpenTelemetry PHP API