Docker container network configuration

Oct 13, 2025 by wbrum.org 34 views

Introduction

Monitoring and metrics collection are crucial components of any modern web application. In this article, we will explore a common issue that arises when trying to collect metrics from a Django application running inside a Docker container using Prometheus. Specifically, we will delve into the problem of Prometheus being unable to scrape Django metrics due to a 400 Bad Request error.

Background

To collect metrics from a Django application, we can use the django-prometheus library, which exposes metrics at a specific endpoint. In this case, the metrics are exposed at http://127.0.0.1:8888/prometheus/metrics. However, when running the Django application inside a Docker container, Prometheus is unable to scrape these metrics, resulting in a 400 Bad Request error.

Problem Statement

The problem can be summarized as follows:

Django application running inside a Docker container
Metrics exposed at http://127.0.0.1:8888/prometheus/metrics
Prometheus unable to scrape metrics due to 400 Bad Request error

Possible Causes

There are several possible causes for this issue:

Docker container network configuration: The Docker container may not be configured to allow incoming requests from Prometheus.
Firewall rules: Firewall rules may be blocking incoming requests from Prometheus.
Django application configuration: The Django application may not be configured to expose metrics at the specified endpoint.
Prometheus configuration: Prometheus may not be configured to scrape metrics from the correct endpoint.

Troubleshooting Steps

To troubleshoot this issue, we can follow these steps:

Verify Docker container network configuration: Ensure that the Docker container is configured to allow incoming requests from Prometheus. This can be done by checking the container's network settings and ensuring that the prometheus service is allowed to connect.
Verify firewall rules: Check the firewall rules to ensure that incoming requests from Prometheus are not being blocked.
Verify Django application configuration: Check the Django application's configuration to ensure that metrics are being exposed at the specified endpoint.
Verify Prometheus configuration: Check the Prometheus configuration to ensure that it is scraping metrics from the correct endpoint.

Solution

After troubleshooting, we can try the following solutions:

Expose metrics on a different endpoint: Try exposing metrics on a different endpoint, such as http://127.0.0.1:8888/metrics.
Use a different Prometheus configuration: Try using a different Prometheus configuration, such as using a different scrape interval or scrape timeout.
Use a different Docker container network configuration: Try using a different Docker container network configuration, such as using a different network or port.

Example Use Case

Here is an example use case:

Django application configuration: In the settings.py file, add the following configuration:

METRICS_URL = '/prometheus/metrics'

Prometheus configuration: In the prometheus.yml file, add the following configuration:

scrape_configs:
  - job_name: 'django'
    scrape_interval: 10s
    metrics_path: '/prometheus/metrics'
    static_configs:
      - targets: ['django:8888']

Docker container configuration: In the docker-compose.yml file, add the following configuration:

version: '3'
services:
  django:
    build: .
    ports:
      - "8888:8888"
    environment:
      - METRICS_URL=/prometheus/metrics

Conclusion

In this article, we explored a common issue that arises when trying to collect metrics from a Django application running inside a Docker container using Prometheus. We identified possible causes for the issue and provided troubleshooting steps and solutions. We also provided an example use case to demonstrate how to configure the Django application, Prometheus, and Docker container to collect metrics successfully.

Additional Resources

For additional resources on this topic, please refer to the following:

Django Prometheus documentation: https://django-prometheus.readthedocs.io/en/latest/
Prometheus documentation: https://prometheus.io/docs/
Docker documentation: https://docs.docker.com/

Monitoring Django applications with Prometheus: https://example.com/monitoring-django-applications-with-prometheus
Collecting metrics from Docker containers with Prometheus: https://example.com/collecting-metrics-from-docker-containers-with-prometheus
Q&A: Prometheus can't scrape Django metrics (400 Bad Request) when running in Docker container =====================================================================================

Q: What is the issue with Prometheus scraping Django metrics in a Docker container?

A: The issue is that Prometheus is unable to scrape Django metrics due to a 400 Bad Request error when running in a Docker container.

Q: What are the possible causes of this issue?

A: There are several possible causes for this issue:

Docker container network configuration: The Docker container may not be configured to allow incoming requests from Prometheus.
Firewall rules: Firewall rules may be blocking incoming requests from Prometheus.
Django application configuration: The Django application may not be configured to expose metrics at the specified endpoint.
Prometheus configuration: Prometheus may not be configured to scrape metrics from the correct endpoint.

Q: How can I troubleshoot this issue?

A: To troubleshoot this issue, you can follow these steps:

Verify Docker container network configuration: Ensure that the Docker container is configured to allow incoming requests from Prometheus. This can be done by checking the container's network settings and ensuring that the prometheus service is allowed to connect.
Verify firewall rules: Check the firewall rules to ensure that incoming requests from Prometheus are not being blocked.
Verify Django application configuration: Check the Django application's configuration to ensure that metrics are being exposed at the specified endpoint.
Verify Prometheus configuration: Check the Prometheus configuration to ensure that it is scraping metrics from the correct endpoint.

Q: What are some common mistakes that can cause this issue?

A: Some common mistakes that can cause this issue include:

Incorrect endpoint: The endpoint specified in the Prometheus configuration may not match the endpoint exposed by the Django application.
Incorrect port: The port specified in the Prometheus configuration may not match the port exposed by the Django application.
Incorrect network configuration: The Docker container may not be configured to allow incoming requests from Prometheus.

Q: How can I expose metrics on a different endpoint?

A: To expose metrics on a different endpoint, you can modify the Django application's configuration to expose metrics at a different endpoint. For example, you can add the following configuration to the settings.py file:

METRICS_URL = '/metrics'

Q: How can I use a different Prometheus configuration?

A: To use a different Prometheus configuration, you can modify the Prometheus configuration to scrape metrics from a different endpoint. For example, you can add the following configuration to the prometheus.yml file:

scrape_configs:
  - job_name: 'django'
    scrape_interval: 10s
    metrics_path: '/metrics'
    static_configs:
      - targets: ['django:8888']

Q: How can I use a different Docker container network configuration?

A: To use a different Docker container network configuration, you can modify the Docker container's network settings to allow incoming requests from Prometheus. For example, you can add the following configuration to the docker-compose.yml file:

version: '3'
services:
  django:
    build: .
    ports:
      - "8888:8888"
    environment:
      - METRICS_URL=/metrics
    networks:
      - prometheus

Q: What are some best practices for monitoring Django applications with Prometheus?

A: Some best practices for monitoring Django applications with Prometheus include:

Use a consistent endpoint: Use a consistent endpoint for exposing metrics to ensure that Prometheus can scrape metrics correctly.
Use a consistent port: Use a consistent port for exposing metrics to ensure that Prometheus can scrape metrics correctly.
Use a consistent network configuration: Use a consistent network configuration to ensure that Prometheus can scrape metrics correctly.
Monitor metrics regularly: Monitor metrics regularly to ensure that the application is performing correctly.

Q: What are some resources for learning more about monitoring Django applications with Prometheus?

A: Some resources for learning more about monitoring Django applications with Prometheus include:

Django Prometheus documentation: https://django-prometheus.readthedocs.io/en/latest/
Prometheus documentation: https://prometheus.io/docs/
Docker documentation: https://docs.docker.com/