---
title: Learn how to instrument Apache Http Server with OpenTelemetry
linkTitle: Instrument Apache Http Server
date: 2022-05-27
spelling:
  cSpell:ignore Centos centos7 Debajit debuggability libmod OLTP uncompress
author: '[Debajit Das](https://github.com/DebajitDas) (Cisco)'
---

If you are using Apache Web Server and in dire need of some observability tool
to monitor your web server, the [OpenTelemetry Apache Module][] is the right
candidate for you: it enables tracing of incoming requests to the server and it
will capture the response time of many modules (including `mod_proxy`) involved
in such an incoming request. With that you will get hierarchical time
consumption by each module. This article demonstrates the monitoring
capabilities of Apache OpenTelemetry Module and quick guide to get started with
the module.

## Getting Started with OpenTelemetry Module

### Building the module

Getting started with the OpenTelemetry module for apache httpd is pretty simple,
all you need is a docker engine and git. Download the source code from github
and then build the docker image on CentOS7:

```sh
git clone https://github.com/open-telemetry/opentelemetry-cpp-contrib
cd  instrumentation/otel-webserver-module
docker-compose --profile centos7 build
```

These commands download all required dependencies, builds the OpenTelemetry
module for Apache and installs the same on the docker image.

**Note**: The above commands might take around 1 hour to complete.

When the build is finished, run the docker image, by typing the following
command:

```sh
docker-compose --profile centos7 up -d
```

The above command starts up the centos7 image in a docker container named
`webserver_centos7` along with the OpenTelemetry Collector and a Zipkin backend.

Apache OpenTelemetry Module will be configured and installed in the desired
location and Apache server will be started with Apache OpenTelemetry Module.

### Viewing spans on the backend

As mentioned in [docker-compose.yml][], `webserver_centos7` listens on port
9004, Zipkin listens on port 9411 and the OpenTelemetry Collector listens on
port 4317.

To send a request to Apache webServer you can either use curl from terminal
(`curl localhost:9004`), or visit [localhost:9004][] in any browser. A default
landing page saying "Testing 123..." for Apache Http Server on Centos will be
displayed as below:

![Testing](testing.png)

Now, traces and spans can be seen on the Zipkin backend. To view them, visit
[localhost:9411][] in your browser and click on **Run Query** button. Following
is the screenshot from Zipkin UI showing spans emitted by the Apache webServer.

![Span-List](span-list.png)

This shows a list of queries or endpoints that have been triggered to Apache
WebServer, such as `/noindex/css`.

To see the details click on any of the **SHOW** buttons. Below is the screenshot
from the Zipkin UI showing the span hierarchy.

![A screenshot from the Zipkin UI showing the span hierarchy](span-hierarchy.png)

The above shows that as a part of this request, `mod_proxy`,
`mod_proxy_balancer` and `mod_dav` got involved in the request processing and
time consumed in each of the modules.

## How can module level details be beneficial?

To demonstrate the benefits of module level details, we'll introduce an
artificial delay in a php script and see how the delay gets displayed in the
Zipkin backend. The following steps are required to be done.

- Login to the container and install the php module.

  ```sh
  docker exec -it webserver_centos7 /bin/bash
  yum install php -y
  ```

- Add `AddType application/x-httpd-php .html` in `/etc/httpd/conf/httpd.conf` as
  mentioned below:

  ![Php-Config](php-config.png)

- Create a file named as `index.html` in the **/var/www/html** directory and add
  the following text

  ```html
  <!DOCTYPE html>
  <html>
    <head>
      <title>PHP Test Page</title>
    </head>

    <body>
      <?php
        echo date('h:i:s') . "<br>"; echo "Introduce delay of 1 seconds" . "<br />";
      sleep(1); echo date('h:i:s'); ?>
    </body>
  </html>
  ```

- Restart the server:

  ```sh
  httpd -k restart
  ```

- Now, visit [localhost:9004/index.html][]. You should see something like this:

  ![Php-Response](php-response.png)

- Now, traces and spans can be seen on the Zipkin backend. To view them, type
  [localhost:9411][] on the browser and click on the **Run Query** Button. To
  see the details, click on the **SHOW** button corresponding to `/index.html`.

  ![Span-Delay](span-delay.png)

- We can see that, `mod_php5.c_handler` consumes around **1 second** which
  contributes to the overall time-consumption of the request.

As the HTTP request flows through individual modules, delay in execution or
errors might occur at any of the modules involved in the request. To identify
the root cause of any delay or errors in request processing, module wise
information (such as response time of individual modules) would enhance the
debuggability of the Apache web server.

## Installing OpenTelemetry Module in Target System

To make use of apache OpenTelemetry module, use the following steps to extract
the package and install on the target system where apache is installed.

- In order to clone the source code, execute the following

  ```sh
  git clone https://github.com/open-telemetry/opentelemetry-cpp-contrib
  cd  opentelemetry-cpp-contrib/instrumentation/otel-webserver-module
  ```

- Trigger the build command to generate the package inside the docker image

  ```sh
  docker-compose --profile centos7 build
  ```

The above might take around an hour to build. This would build on Centos 7 image
as `apache_centos7`

- Once the build is complete, it's time to extract the image. We need to startup
  the container which can be done by the following command

  ```sh
  docker run -idt --name <container_name> apache_centos7 /bin/bash
  ```

The above command would run the container and can be verified using the
`docker ps` command.

- The generated package inside the container is available inside
  `/otel-webserver-module/build` directory. The same can be extracted to the
  host system as

  ```sh
  docker cp <container_name>:/otel-webserver-module/build/opentelemetry-webserver-sdk-x64-linux.tgz <target-directory>
  ```

**Note:** The above package should work on any linux distribution having
**x86-64** instruction set and glibc version greater than 2.17. At the point of
writing this blog, support for other architectures is not provided.

- Transfer the above package along with [opentelemetry_module.conf][] to the
  target system.

- Uncompress the package `opentelemetry-webserver-sdk-x64-linux.tgz` to `/opt`
  directory.

  ```sh
  tar -xvf opentelemetry-webserver-sdk-x64-linux.tgz -C /opt
  ```

- Now, install the module by executing the following

  ```sh
  cd /opt/opentelemetry-webserver-sdk
  ./install.sh
  ```

- In the case of Centos, apache configuration is generally located in
  `/etc/httpd/conf/`. Hence copy the [opentelemetry_module.conf][] to
  `/etc/httpd/conf`.

- Edit the `/etc/httpd/conf/httpd.conf` and add
  `Include conf/opentelemetry_module.conf` at the end of the file as mentioned
  below:

  ![Conf](conf.png)

- Now let’s look at opentelemetry_module.conf and its contents:

  - The below LoadFile are the dependent libraries that come with the package.

    ![LoadFile](loadfile.png)

  - The below configuration are for the OpenTelemetry Module

    ![LoadModule](loadmodule.png)

    In the case of Apache 2.2, `libmod_apache_otel22.so` needs to be used
    instead of `libmod_apache_otel.so`

  - The following directive should be ON for the openTelemetry module to be
    enabled, else it would be disabled.

    ![enabled](enabled.png)

  - Since the module works with the Collector and sends data in OLTP format, the
    following directives are necessary.

    ![exporter](exporter.png)

    _ApacheModuleOtelExporterEndpoint_ should point to the endpoint of the
    collector

  - ServiceNamespace, ServiceName and ServiceInstanceId should be provided by
    the following directives.

    ![service](service.png)

  - All other directives are either optional and can be kept as it is for this
    guide

- To verify whether Apache OpenTelemetry Module is properly enabled into Apache
  Web Server, type `httpd -M` and look for `otel_apache_module (shared)`

  ![verify-module](verify-module.png)

- Now, restart the apache module and open telemetry module should be
  instrumented.

[docker-compose.yml]:
  https://github.com/open-telemetry/opentelemetry-cpp-contrib/blob/main/instrumentation/otel-webserver-module/docker-compose.yml
[localhost:9004]: http://localhost:9004
[localhost:9004/index.html]: http://localhost:9004/index.html
[localhost:9411]: http://localhost:9411
[opentelemetry_module.conf]:
  https://github.com/open-telemetry/opentelemetry-cpp-contrib/blob/main/instrumentation/otel-webserver-module/opentelemetry_module.conf
[opentelemetry apache module]:
  https://github.com/open-telemetry/opentelemetry-cpp-contrib/tree/main/instrumentation/otel-webserver-module
