Analyze Logs in Graylog

Introduction

In this lab, you will learn how to use Graylog, a powerful open-source log management platform, for collecting and analyzing log data. Centralized logging is a critical component of cybersecurity, allowing you to monitor system events, detect anomalies, and investigate security incidents from a single interface.

You will start by deploying the entire Graylog stack, which includes MongoDB and OpenSearch (the modern replacement for Elasticsearch), using Docker Compose. You will then configure Graylog to receive log data, send sample logs to it, perform search queries to filter information, and finally, build a visual dashboard to monitor key metrics. By the end of this lab, you will have hands-on experience with the fundamental workflow of log analysis in Graylog.

Deploy Graylog with Docker Compose

In this first step, you will deploy the Graylog logging platform. We will use Docker Compose v2, a tool for defining and running multi-container Docker applications. This approach simplifies the setup process by managing all the necessary components—Graylog, OpenSearch, and MongoDB—with a single configuration file.

First, let's prepare the environment and launch the services.

1. The setup script has already installed Docker Compose v2 for you. You can verify the installation by checking its version.

   docker compose version

   You should see an output indicating the Docker Compose version, similar to this:

   Docker Compose version v2.29.7

2. Navigate to the dedicated directory for your Graylog configuration. This helps keep your project organized.

   cd /home/labex/project/graylog

3. Next, create the docker-compose.yml configuration file using the nano text editor. This file tells Docker Compose which containers to run and how to configure them.

   nano docker-compose.yml

4. Copy and paste the following YAML configuration into the nano editor. This configuration defines three services:

   • mongodb: Stores Graylog's configuration data.
   • opensearch: Indexes and stores the log messages for fast searching. Note that OpenSearch 2.12+ requires an initial admin password.
   • graylog: The main application, providing the web interface and log processing engine.

   services:
     mongodb:
       image: mongo:6.0
       container_name: graylog_mongodb
       volumes:
         - mongo_data:/data/db
       networks:
         - graylog_network
       healthcheck:
         test: ["CMD", "mongosh", "--eval", "db.runCommand('ping').ok"]
         interval: 30s
         timeout: 10s
         retries: 3
     opensearch:
       image: opensearchproject/opensearch:2.13.0
       container_name: graylog_opensearch
       environment:
         - discovery.type=single-node
         - plugins.security.disabled=true
         - bootstrap.memory_lock=true
         - "OPENSEARCH_JAVA_OPTS=-Xms512m -Xmx512m"
         - "OPENSEARCH_INITIAL_ADMIN_PASSWORD=StrongPassword123!"
       ulimits:
         memlock:
           soft: -1
           hard: -1
       volumes:
         - opensearch_data:/usr/share/opensearch/data
       networks:
         - graylog_network
       healthcheck:
         test:
           [
             "CMD-SHELL",
             "curl -f http://localhost:9200/_cluster/health || exit 1"
           ]
         interval: 30s
         timeout: 10s
         retries: 3
     graylog:
       image: graylog/graylog:6.1
       container_name: graylog_server
       volumes:
         - graylog_data:/usr/share/graylog/data
       environment:
         - GRAYLOG_PASSWORD_SECRET=somepasswordpepper
         - GRAYLOG_ROOT_PASSWORD_SHA2=8c6976e5b5410415bde908bd4dee15dfb167a9c873fc4bb8a81f6f2ab448a918
         - GRAYLOG_HTTP_EXTERNAL_URI=http://127.0.0.1:9000/
         - GRAYLOG_ELASTICSEARCH_HOSTS=http://opensearch:9200
         - GRAYLOG_MONGODB_URI=mongodb://mongodb:27017/graylog
       depends_on:
         mongodb:
           condition: service_healthy
         opensearch:
           condition: service_healthy
       ports:
         - "9000:9000"
         - "1514:1514"
         - "1514:1514/udp"
         - "12201:12201"
         - "12201:12201/udp"
       networks:
         - graylog_network
   volumes:
     mongo_data:
     opensearch_data:
     graylog_data:
   networks:
     graylog_network:
       driver: bridge

   Press Ctrl+O, then Enter to save the file, and Ctrl+X to exit nano.

5. Now, start all the services in the background using the -d (detached) flag.

   docker compose up -d

6. It may take a minute or two for all services to initialize. You can check the status of your containers to ensure they are running correctly.

   docker compose ps

   You should see all three services (graylog_server, graylog_opensearch, graylog_mongodb) with a State of Up.

   NAME                 IMAGE                                 COMMAND                  SERVICE      CREATED              STATUS                        PORTS
   graylog_mongodb      mongo:6.0                             "docker-entrypoint.s…"   mongodb      About a minute ago   Up About a minute (healthy)   27017/tcp
   graylog_opensearch   opensearchproject/opensearch:2.13.0   "./opensearch-docker…"   opensearch   About a minute ago   Up About a minute (healthy)   9200/tcp, 9300/tcp, 9600/tcp, 9650/tcp
   graylog_server       graylog/graylog:6.1                   "tini -- /docker-ent…"   graylog      About a minute ago   Up 34 seconds (healthy)       0.0.0.0:1514->1514/tcp, :::1514->1514/tcp, 0.0.0.0:9000->9000/tcp, 0.0.0.0:1514->1514/udp, :::9000->9000/tcp, :::1514->1514/udp, 0.0.0.0:12201->12201/tcp, 0.0.0.0:12201->12201/udp, :::12201->12201/tcp, :::12201->12201/udp

The Graylog web interface is now accessible. You have successfully deployed the Graylog stack and are ready to configure it.

Configure a Syslog Input

With Graylog running, the next step is to configure an "Input." An input is a component that tells Graylog how to accept log messages. For this lab, you will create a Syslog UDP input, which is a common standard for collecting logs from network devices and Linux/Unix servers.

1. Open the Graylog web interface in your browser. You can do this by clicking the "Web Terminal" tab and selecting "Desktop" to open the browser, or by using the dedicated browser icon in the lab environment. Navigate to the following URL:

   http://127.0.0.1:9000

   

2. Log in with the default credentials:

   • Username: admin
   • Password: admin

3. Once logged in, you will create the new input. In the top navigation bar, click on System, and then select Inputs from the dropdown menu.

4. On the Inputs page, find the "Syslog UDP" input type in the "Select input" dropdown list and click the Launch new input button next to it.

5. A modal window will appear. Fill in the form with the following details to configure the input:

   • Node: Select the only available node from the dropdown (it will be your Graylog server).
   • Title: Syslog UDP Input (This is a descriptive name for your input).
   • Bind address: 0.0.0.0 (This tells Graylog to listen for logs on all network interfaces of the container).
   • Port: 1514 (This is the port where Graylog will listen for incoming syslog messages).

   Leave all other settings as their defaults and click Save.

6. After saving, you will be returned to the Inputs page. Your new "Syslog UDP Input" should appear in the list with a green "Running" status, indicating that it is active and ready to receive data.

7. To test the input, return to your terminal and send a sample log message using the netcat (nc) utility. This command constructs a basic syslog message and sends it to the UDP port 1514 on your local machine.

   echo "<14>$(date +'%b %d %H:%M:%S') localhost labex: Test syslog message" | nc -w1 -u 127.0.0.1 1514

You have now successfully configured Graylog to receive logs. In the next step, you will send more structured logs and learn how to view them in the Graylog interface.

Send and View Sample Logs

Now that your Syslog input is ready, it's time to generate and send a batch of sample logs. This will populate Graylog with data, allowing you to practice searching and analysis. You will create a simple shell script to simulate log messages from an application.

1. First, navigate back to your project's root directory in the terminal.

   cd /home/labex/project

2. Create a new shell script named generate_logs.sh using the nano editor.

   nano generate_logs.sh

3. Copy and paste the following script into the editor. This script generates 10 log messages in a loop. Each message has a random severity level, a timestamp, and a simple message body. It then uses nc to send each log to the Graylog input you configured.

   #!/bin/bash
   for i in {1..10}; do
     severity=$(((RANDOM % 8)))
     timestamp=$(date +'%b %d %H:%M:%S')
     echo "<$((severity + 8))>$timestamp localhost sample_app[$i]: Sample log message $i with severity $severity" | nc -w1 -u 127.0.0.1 1514
     echo "Sent log message $i"
     sleep 1
   done

   Press Ctrl+O, Enter, and Ctrl+X to save and exit.

4. Make the script executable using the chmod command.

   chmod +x generate_logs.sh

5. Run the script to send the logs to Graylog.

   ./generate_logs.sh

   You will see output in your terminal as each log is sent.

   Sent log message 1
   Sent log message 2
   ...
   Sent log message 10

6. Now, let's view these logs in Graylog. Go back to the Graylog web interface in your browser (http://127.0.0.1:9000).

7. Click on the Search tab in the top navigation bar. You should see the log messages you just sent appear in the "Messages" list. It might take a few seconds for them to be indexed and displayed.

   You can see how Graylog automatically parses the messages, breaking them down into fields like timestamp, source, application_name, and severity. This structured data is key to effective log analysis.

Query and Analyze Log Data

With logs flowing into Graylog, you can now learn how to search and filter them. Graylog's search functionality is powerful and allows you to quickly pinpoint specific events. This is essential for troubleshooting issues or investigating security incidents.

1. Go to the Search page in the Graylog web interface. The search bar is at the top of the page.

2. Let's start with a simple query. To find all logs from your simulated application, type the following into the search bar and press Enter:

   application_name:sample_app

   This filters the results to show only the logs where the application_name field is exactly sample_app.

3. Now, try some other queries to explore different filtering capabilities:

   • Find logs with a specific severity level (e.g., level 4):
     severity:4
   • Find logs with a severity level greater than 5 (warnings, errors, etc.):
     severity:>5
   • Search for a phrase within the log message:
     message:"log message 5"
   • Combine filters using AND:
     application_name:sample_app AND severity:<3

4. You can also control the time frame of your search. By default, Graylog shows logs from the "Last 5 minutes". Click on the time range selector to the left of the search bar and change it to Last 30 minutes to ensure all your generated logs are included in the search results.

5. To make a frequently used query easily accessible, you can save it. Let's save a search for high-severity events.

   • Run the query: severity:>4
   • To the right of the search bar, click the floppy disk icon (Save Search).
   • In the "Save Search" dialog, enter a Title, for example, High Severity Events.
   • Click Save.

   You can now access this saved search anytime from the "Saved Searches" list on the left sidebar, allowing you to quickly check for critical events.

Build a Monitoring Dashboard

While the search page is great for active investigation, dashboards provide an at-a-glance overview of your log data. In this final step, you will create a dashboard with several widgets to visualize key metrics from your logs.

1. In the Graylog web interface, navigate to the Dashboards section from the top menu.

2. Click the Create dashboard button.

   • Enter a Title: Application Health Dashboard
   • Enter a Description: Monitors the health and activity of sample_app.
   • Click Create.

3. You now have an empty dashboard. Let's add some widgets to it. Click the Unlock / Edit button to enter edit mode.

4. Add a "Log Count" Widget: This widget will show the total number of log messages over time.

   • Click Create Widget for Dashboard.
   • Select Aggregation as the widget type.
   • In the configuration window:
     • Title: Total Log Volume
     • Under "Rows", select timestamp as the field.
     • Choose Bar Chart as the visualization type.
   • Click Create.

5. Add a "Severity Distribution" Widget: This widget will show the breakdown of logs by severity level.

   • Click Create Widget for Dashboard again.
   • Select Aggregation as the widget type.
   • In the configuration window:
     • Title: Log Severity Distribution
     • Under "Rows", select severity as the field.
     • Choose Pie Chart as the visualization type.
   • Click Create.

6. Add a "Recent Messages" Widget: This widget will display a list of the most recent log messages.

   • Click Create Widget for Dashboard.
   • Select Messages as the widget type.
   • In the configuration window:
     • Title: Recent Log Messages
     • In the "Streams" field, make sure All messages is selected.
   • Click Create.

7. Once you have added the widgets, you can drag and drop them to arrange the layout. You can also resize them by dragging their corners. Arrange them in a way that is easy to read.

8. When you are satisfied with the layout, click the Lock / Save button in the top right corner to save your dashboard.

You have now created a basic monitoring dashboard. In a real-world scenario, dashboards like this are invaluable for keeping an eye on system health and security posture.

Summary

In this lab, you gained practical experience with the core functionalities of Graylog for log management and analysis. You started by deploying a complete Graylog environment using Docker Compose, which included the Graylog server, OpenSearch, and MongoDB.

You then configured a Syslog input to enable log collection and used a script to send sample log data, simulating real-world application logs. You learned how to use Graylog's powerful search and query language to filter and find specific information within your logs. Finally, you brought it all together by building a custom dashboard with various widgets to visualize log metrics, providing an at-a-glance view of system activity. These skills form a solid foundation for using Graylog in cybersecurity monitoring and operational intelligence.