Monitoring Remote Network Health: Building a Lightweight Connectivity Tool with Bash and Docker

Have you ever needed to verify if your remote servers have outbound internet access? Whether you're managing a cluster of web servers or a set of edge devices, ensuring they can "talk to the world" is a fundamental task.

In this post, I'll walk you through a lightweight Network Connectivity Monitoring Tool I built using Bash. It's simple, portable, and comes with a Docker-based test environment to get you started safely.

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The Problem

Manually SSH-ing into dozens of servers to run a ping command is tedious and error-prone. I needed a way to:

1. Check connectivity from multiple servers at once.
2. Support non-standard SSH ports.
3. Log results for historical tracking.
4. Get a quick summary of which hosts are "Reachable" vs "Unreachable."

The Solution: A Bash-Powered Monitor

The core of this tool is a Bash script that uses SSH to execute a ping command on remote targets. Here's a look at the key features and how it works.

1. Robust Scripting with set -euo pipefail

To make the script reliable, I used strict error handling:

• -e: Exit immediately if a command fails.
• -u: Treat unset variables as errors.
• -o pipefail: Ensure that if any part of a pipeline fails, the whole pipeline fails.

2. Intelligent Connectivity Checks

The script doesn't just check if the server is "up"; it distinguishes between an SSH failure (can't connect to the box) and a Network failure (connected to the box, but the box can't reach the internet).

# A snippet of the core logic
if ssh -o StrictHostKeyChecking=no -o BatchMode=yes -p "${port}" "${ssh_target}" \
       "ping -c 3 8.8.8.8 > /dev/null 2>&1"; then
    log_result "$host" "REACHABLE" "$TIMESTAMP"
    echo "  ✓ $host - REACHABLE"
else
    log_result "$host" "UNREACHABLE" "$TIMESTAMP"
    echo "  ✗ $host - UNREACHABLE (network issue)"
fi

3. Automated Logging & Summaries

Every run generates a timestamped log in connectivity_log.txt, making it easy to spot patterns over time. At the end of each run, you get a clean summary:

========================================
  Summary
========================================
  Total hosts checked: 3
  Reachable:          2
  Unreachable:        1
========================================

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Testing Safely with Docker

One of the best parts of this project is the included Test Lab. Using docker-compose, you can spin up three Ubuntu-based SSH servers locally to test the script without risking your production environment.

I've included a setup.sh script that:

• Starts the containers.
• Installs ping (not present in minimal Ubuntu images).
• Configures SSH keys for passwordless login.
• Validates the environment.

How to Try It Out

1. Clone the project.
2. Generate an SSH key if you haven't already: ssh-keygen -t rsa.

3. Launch the test lab:
   

   ./setup.sh
   

4. Run the monitor:
   

   ./monitor_connectivity.sh
   

Lessons Learned

While building this, I ran into a few classic Bash "gotchas":

• Loops vs set -e: Using a while read loop with set -e can cause the script to exit prematurely when it hits the end of a file. Switching to a for loop with grep solved this.
• Docker Ephemerality: Since containers reset on restart, I automated the SSH key injection into the setup.sh script to ensure a smooth developer experience.

Conclusion

Sometimes, the simplest tools are the most effective. This Bash script provides a no-nonsense way to monitor network health across your infrastructure.

Check out the full source code here! github

What are your favorite "mini-tools" for server management? Let me know in the comments!