Debugging and docker containers

When running web applications in a Docker container, it’s often useful to be able to view the logs generated by the application. One common way to do this is to have Apache or NGINX output its logs to the Docker logs. This way, you can use the docker logs command to view the logs generated by Apache, making it easy to troubleshoot issues or monitor the performance of your application.

Docker logs

Docker logs are a feature of the Docker platform that allows you to view the output of a container’s stdout and stderr streams. This can be useful for troubleshooting issues, monitoring the performance of your application, and understanding the behaviour of your containerised applications.

When a container is running, any output sent to stdout and stderr is captured by the Docker daemon and stored in a buffer. This buffer is then made available through the docker logs command, which allows you to view the output of the container’s stdout and stderr streams. The docker logs command also allows you to specify options such as the number of lines to display, and whether to follow the logs in real-time. Additionally, it’s possible to configure a log driver to send logs to different external systems like syslog or a cloud-based log management service. The entire reference can be found here.

docker logs -f containername

The docker logs command is a powerful tool that can help you to quickly understand what is happening within your containers. By viewing the output of the container’s stdout and stderr streams, you can quickly identify issues and understand how your containerised application is behaving. Additionally, this feature enables you to have a centralised log management that can be helpful for troubleshooting, auditing and compliance.

Apache

To configure Apache to output its logs to Docker, you’ll first need to make sure that Apache is running in a container. Once you have Apache running in a container, you’ll need to edit the Apache configuration file (usually located at /etc/httpd/conf/httpd.conf) to change the location of the log files. Instead of logging to a file on the host machine, you’ll need to configure Apache to log to the standard output (stdout) and standard error (stderr) streams.

Here’s an example of how you might configure Apache to log to stdout and stderr in the httpd.conf file:

CustomLog "|/usr/bin/tee -a /proc/self/fd/1" combined
ErrorLog "|/usr/bin/tee -a /proc/self/fd/2"

This tells Apache to pipe its log output to the tee command, which in turn pipes the output to both the specified file and to the standard output and standard error streams.

Once you’ve made these changes, you’ll need to rebuild the image and then restart the Apache container for the changes to take effect. From this point forward, all of Apache’s log output will be sent to the Docker logs, and you can use the docker logs command to view the logs.

It’s worth noting that there are other ways to configure Apache to output its logs to Docker, and this will depend on your specific use case and the version of Apache you are running. But the above should give you a good starting point for getting Apache to output its logs to Docker logs.

NGINX

The first step is to make sure that NGINX is running in a container. Once you have NGINX running in a container, you’ll need to edit the NGINX configuration file (usually located at /etc/nginx/nginx.conf) to change the location of the log files. Instead of logging to a file on the host machine, you’ll need to configure NGINX to log to the standard output (stdout) and standard error (stderr) streams.

Here’s an example of how you might configure NGINX to log to stdout and stderr in the nginx.conf file:

http {
    ...
    access_log /dev/stdout;
    error_log /dev/stderr;
    ...
}

This tells NGINX to log the access log and error log to the standard output and standard error streams respectively.

Once you’ve made these changes, you’ll need to rebuild the docker image and restart the NGINX container for the changes to take effect. From this point forward, all of NGINX’s log output will be sent to the Docker logs, and you can use the docker logs command to view the logs.

It’s worth noting that there are other ways to configure NGINX to output its logs to Docker, and this will depend on your specific use case and the version of NGINX you are running. If you need more help with this, don’t hesitate to contact us.

Conclusion

Directing the logs to be output to Docker logs can be a useful way to troubleshoot issues and monitor the performance of your web application. Now, you can easily view the logs using the docker logs command, making it easier to debug and monitor your application.