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Saniyat Hossain
Saniyat Hossain

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Essential Debugging Techniques for Network and Service Connectivity

In the fast-paced world of software development, effective debugging is crucial for ensuring smooth operations and quick resolutions to issues. This article provides practical examples and tips for using essential tools like curl, telnet, and tcpdump, along with connectivity checks for services such as Redis, MySQL, RabbitMQ, Minio, and more. We'll also cover additional tricks for extensive debugging and discuss tools like NGINX and HAProxy.

Tools and Techniques Overview

Curl: The Versatile HTTP Client

curl is a powerful command-line tool for transferring data with URLs. It supports various protocols and provides extensive options for debugging.

Basic Usage:

curl -I http://example.com
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Verbose Mode with SSL Verification and Proxy:

curl -kvvv --proxy http://proxy.example.com:8080 https://example.com
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Example Response:

* Rebuilt URL to: https://example.com/
*   Trying 93.184.216.34...
* TCP_NODELAY set
* Connected to example.com (93.184.216.34) port 443 (#0)
> GET / HTTP/1.1
> Host: example.com
> User-Agent: curl/7.68.0
> Accept: */*
< HTTP/1.1 200 OK
...
* Connection #0 to host example.com left intact
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Tips and Tricks:

  1. Check Headers and Content: 
   curl -i http://example.com
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  1. Follow Redirects: 
   curl -L http://example.com
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  1. Download File: 
   curl -O http://example.com/file.zip
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  1. Send Data with POST: 
   curl -d "param1=value1&param2=value2" -X POST http://example.com/submit
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  1. Use with Authentication: 
   curl -u username:password http://example.com
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  1. Custom Headers: 
   curl -H "Custom-Header: value" http://example.com
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  1. Debugging DNS: 
   curl --dns-servers 8.8.8.8 http://example.com
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  1. Output to File: 
   curl http://example.com -o output.txt
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  1. Testing APIs: 
   curl -X POST -H "Content-Type: application/json" -d '{"key1":"value1", "key2":"value2"}' http://api.example.com/endpoint
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Telnet: Simple Connectivity Testing

telnet is useful for testing connectivity to remote hosts and services.

Basic Usage:

telnet example.com 80
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Example Response:

Trying 93.184.216.34...
Connected to example.com.
Escape character is '^]'.
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Tips and Tricks:

  1. Check SMTP Server: 
   telnet smtp.example.com 25
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  1. Test HTTP Service: 
   telnet example.com 80
   GET / HTTP/1.1
   Host: example.com
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  1. Escape Character: 
   telnet example.com 80
   (Ctrl + ])
   quit
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Tcpdump: Network Packet Analyzer

tcpdump captures network packets for detailed analysis.

Basic Usage:

sudo tcpdump -i eth0
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Capture Specific Traffic:

sudo tcpdump -i eth0 'tcp port 80'
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Tips and Tricks:

  1. Save to File: 
   sudo tcpdump -i eth0 -w capture.pcap
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  1. Read from File: 
   sudo tcpdump -r capture.pcap
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  1. Filter by Host: 
   sudo tcpdump -i eth0 host example.com
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  1. Filter by Port: 
   sudo tcpdump -i eth0 port 443
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  1. Analyze HTTP Traffic: 
   sudo tcpdump -i eth0 -A -s 0 'tcp port 80'
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  1. Limit Packet Capture: 
   sudo tcpdump -c 100 -i eth0
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Ping: Network Latency Checker

Basic Usage:

ping example.com
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Example Response:

PING example.com (93.184.216.34) 56(84) bytes of data.
64 bytes from example.com (93.184.216.34): icmp_seq=1 ttl=54 time=6.67 ms
64 bytes from example.com (93.184.216.34): icmp_seq=2 ttl=54 time=6.73 ms
...
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SFTP: Secure File Transfer Protocol

Basic Usage:

sftp user@example.com
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Example Response:

Connected to example.com.
sftp>
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Wireshark: Network Protocol Analyzer

Wireshark is a GUI tool for capturing and analyzing network traffic.

Basic Usage:

  1. Open Wireshark.
  2. Select the network interface to capture traffic.
  3. Use filters (e.g., http, tcp.port == 80) to refine the capture.

Elasticsearch and Kibana: Search and Analytics Engine

Elasticsearch Basic Usage:

curl -X GET "localhost:9200"
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Example Response:

{
  "name" : "node-1",
  "cluster_name" : "elasticsearch",
  "cluster_uuid" : "XYZ123",
  ...
}
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Kibana Basic Usage:

Open a web browser and navigate to http://localhost:5601.

Jenkins: Continuous Integration and Delivery

Basic Usage:

Navigate to Jenkins web interface at http://localhost:8080.

Service Connectivity and Authentication Checks

Docker Container Setup

Dockerfile Example 

# Use a slim base image
FROM debian:slim-buster

# Install necessary packages
RUN apt-get update && apt-get install -y \
    curl \
    telnet \
    tcpdump \
    mysql-client \
    redis-tools \
    rabbitmq-server \
    mc \
    td-agent \
    postgresql-client \
    --no-install-recommends && \
    rm -rf /var/lib/apt/lists/*

CMD ["bash"]
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Connectivity Checks

Redis

Installation:

Inside Docker Container:

RUN apt-get update && apt-get install -y redis-tools
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Host Machines (Ubuntu, Windows, CentOS/RedHat, Kali Linux):

sudo apt-get update && sudo apt-get install -y redis-tools
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Check Connection:

redis-cli -h redis.example.com -p 6379 ping
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Possible Response:

PONG
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Tips and Tricks:

  1. Check Connection: 
   redis-cli -h redis.example.com -p 6379 ping
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  1. Test with Password: 
   redis-cli -h redis.example.com -p 6379 -a password ping
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MySQL

Installation:

Inside Docker Container:

RUN apt-get update && apt-get install -y mysql-client
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Host Machines (Ubuntu, Windows, CentOS/RedHat, Kali Linux):

sudo apt-get update && sudo apt-get install -y mysql-client
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Check Connection:

mysql -h mysql.example.com -P 3306 -u username -p
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Possible Response:

Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 8
Server version: 5.7.33 MySQL Community Server (GPL)
...
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Tips and Tricks:

  1. Check Connection: 
   mysql -h mysql.example.com -P 3306 -u username -p
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  1. Test with Database: 
   mysql -h mysql.example.com -P 3306 -u username -p database_name
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RabbitMQ

Installation:

Inside Docker Container:

RUN apt-get update && apt-get install -y rabbitmq-server
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Host Machines (Ubuntu, Windows, CentOS/RedHat, Kali Linux):

sudo apt-get update && sudo apt-get install -y rabbitmq-server
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Check Connection:

curl -kvvv -u guest:guest http://rabbitmq.example.com:15672/api/overview
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Possible Response:

*   Trying rabbitmq.example.com...
* TCP_NODELAY set
* Connected to rabbitmq.example.com (93.184.216.34) port 15672 (#0)
> GET /api/overview HTTP/1.1
> Host: rabbitmq.example.com
> Authorization: Basic Z3Vlc3Q6Z3Vlc3Q=
> User-Agent: curl/

7.68.0
> Accept: */*
< HTTP/1.1 200 OK
...
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Tips and Tricks:

  1. Check Connection: 
   curl -kvvv -u guest:guest http://rabbitmq.example.com:15672/api/overview
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  1. Check Queues: 
   curl -kvvv -u guest:guest http://rabbitmq.example.com:15672/api/queues
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Minio

Installation:

Inside Docker Container:

RUN apt-get update && apt-get install -y mc
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Host Machines (Ubuntu, Windows, CentOS/RedHat, Kali Linux):

sudo apt-get update && sudo apt-get install -y mc
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Check Connection:

curl -kvvv http://minio.example.com:9000
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Possible Response:

*   Trying minio.example.com...
* TCP_NODELAY set
* Connected to minio.example.com (93.184.216.34) port 9000 (#0)
> GET / HTTP/1.1
> Host: minio.example.com
> User-Agent: curl/7.68.0
> Accept: */*
< HTTP/1.1 200 OK
...
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Tips and Tricks:

  1. Check Connection: 
   curl -kvvv http://minio.example.com:9000
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  1. List Buckets: 
   curl -kvvv http://minio.example.com:9000/minio/health/ready
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Fluentd/TD-Agent: Log Management

Installation:

Inside Docker Container:

RUN apt-get update && apt-get install -y td-agent
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Host Machines (Ubuntu, Windows, CentOS/RedHat, Kali Linux):

curl -L https://toolbelt.treasuredata.com/sh/install-ubuntu-bionic-td-agent3.sh | sh
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Check Connection:

curl -kvvv http://fluentd.example.com:24224
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Possible Response:

*   Trying fluentd.example.com...
* TCP_NODELAY set
* Connected to fluentd.example.com (93.184.216.34) port 24224 (#0)
> GET / HTTP/1.1
> Host: fluentd.example.com
> User-Agent: curl/7.68.0
> Accept: */*
< HTTP/1.1 200 OK
...
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Tips and Tricks:

  1. Check Connection: 
   curl -kvvv http://fluentd.example.com:24224
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  1. Check Logs: 
   tail -f /var/log/td-agent/td-agent.log
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Kafka: Distributed Streaming Platform

Installation:

Inside Docker Container:

RUN apt-get update && apt-get install -y kafka
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Host Machines (Ubuntu, Windows, CentOS/RedHat, Kali Linux):

sudo apt-get update && sudo apt-get install -y kafka
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Check Connection:

kafka-console-consumer.sh --bootstrap-server kafka.example.com:9092 --topic test --from-beginning
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Possible Response:

...
Message 1
Message 2
...
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Tips and Tricks:

  1. Check Connection: 
   kafka-console-consumer.sh --bootstrap-server kafka.example.com:9092 --topic test --from-beginning
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  1. Check Topics: 
   kafka-topics.sh --list --bootstrap-server kafka.example.com:9092
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PostgreSQL

Installation:

Inside Docker Container:

RUN apt-get update && apt-get install -y postgresql-client
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Host Machines (Ubuntu, Windows, CentOS/RedHat, Kali Linux):

sudo apt-get update && sudo apt-get install -y postgresql-client
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Check Connection:

psql -h postgres.example.com -p 5432 -U username -d database_name
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Possible Response:

Password for user username:
psql (13.3 (Ubuntu 13.3-1.pgdg20.04+1))
Type "help" for help.

database_name=>
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Tips and Tricks:

  1. Check Connection: 
   psql -h postgres.example.com -p 5432 -U username -d database_name
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  1. List Databases: 
   psql -h postgres.example.com -p 5432 -U username -c "\l"
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NGINX: Web Server Debugging

Configuration Testing:

nginx -t
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Reload Configuration:

sudo systemctl reload nginx
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Log Files:

Access Log:

tail -f /var/log/nginx/access.log
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Error Log:

tail -f /var/log/nginx/error.log
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Debugging Tips:

  1. Check Server Status: 
   curl -I http://localhost
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  1. Verify Configuration Syntax: 
   nginx -t
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  1. Test Specific Configuration File: 
   nginx -c /etc/nginx/nginx.conf
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  1. Check Connection Limit: 
   curl -I --limit-rate 1k http://localhost
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  1. Analyze Request Headers: 
   curl -I http://localhost -H "Host: example.com"
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HAProxy: Load Balancer Debugging

Configuration Testing:

haproxy -c -f /etc/haproxy/haproxy.cfg
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Reload Configuration:

sudo systemctl reload haproxy
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Log Files:

Access Log:

tail -f /var/log/haproxy.log
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Debugging Tips:

  1. Check Frontend Status: 
   curl -I http://haproxy.example.com
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  1. Verify Configuration Syntax: 
   haproxy -c -f /etc/haproxy/haproxy.cfg
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  1. View Statistics: 
   curl http://haproxy.example.com/stats
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  1. Check Backend Health: 
   curl http://haproxy.example.com:8080/health
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  1. Analyze Headers: 
   curl -I http://haproxy.example.com -H "X-Forwarded-For: 1.2.3.4"
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Wireshark: Network Protocol Analyzer

Wireshark is a GUI tool for capturing and analyzing network traffic.

Basic Usage:

  1. Open Wireshark.
  2. Select the network interface to capture traffic.
  3. Use filters (e.g., http, tcp.port == 80) to refine the capture.

Elasticsearch and Kibana: Search and Analytics Engine

Elasticsearch Basic Usage:

curl -X GET "localhost:9200"
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Example Response:

{
  "name" : "node-1",
  "cluster_name" : "elasticsearch",
  "cluster_uuid" : "XYZ123",
  ...
}
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Kibana Basic Usage:

Open a web browser and navigate to http://localhost:5601.

Jenkins: Continuous Integration and Delivery

Basic Usage:

Navigate to Jenkins web interface at http://localhost:8080.

Summary Table

Here's the summarized table of tools and connectivity checks with proper formatting:

Tool / Service Usage Example Command / Response Tips and Tricks
Curl HTTP Client curl -I http://example.com Check headers, follow redirects, send data with POST, use with authentication, custom headers, debugging DNS
Telnet Simple Connectivity Testing telnet example.com 80 Check SMTP server, test HTTP service, escape character
Tcpdump Network Packet Analyzer sudo tcpdump -i eth0 Save to file, read from file, filter by host and port, analyze HTTP traffic
Ping Network Latency Checker ping example.com Basic usage, measure latency
SFTP Secure File Transfer Protocol sftp user@example.com Basic usage, file transfers
Wireshark Network Protocol Analyzer GUI-based tool Capture network traffic, use filters, analyze protocols
Elasticsearch Search and Analytics Engine curl -X GET "localhost:9200" Check cluster status, use Kibana for visual analytics
Jenkins Continuous Integration and Delivery Navigate to Jenkins web interface at http://localhost:8080 Automate builds and deployments, integrate with various tools
Redis Key-Value Store redis-cli -h redis.example.com -p 6379 ping Check connection, test with password
MySQL Relational Database mysql -h mysql.example.com -P 3306 -u username -p Check connection, test with database
RabbitMQ Message Broker curl -kvvv -u guest:guest http://rabbitmq.example.com:15672/api/overview Check connection, check queues
Minio Object Storage curl -kvvv http://minio.example.com:9000 Check connection, list buckets
Fluentd / TD-Agent Log Management curl -kvvv http://fluentd.example.com:24224 Check connection, check logs
Kafka Distributed Streaming Platform kafka-console-consumer.sh --bootstrap-server kafka.example.com:9092 --topic test --from-beginning Check connection, check topics
PostgreSQL Relational Database psql -h postgres.example.com -p 5432 -U username -d database_name Check connection, list databases
NGINX Web Server Debugging nginx -t Verify configuration, reload configuration, check logs
HAProxy Load Balancer Debugging haproxy -c -f /etc/haproxy/haproxy.cfg Verify configuration, reload configuration, view statistics

Conclusion

By leveraging tools like curl, telnet, tcpdump, and others, and understanding how to check connectivity for services such as Redis, MySQL, RabbitMQ, and Minio, you can effectively diagnose and resolve network and service-related issues. Additionally, using NGINX and HAProxy debugging tips can help you maintain a smooth and efficient development workflow.

Feel free to share your thoughts and experiences in the comments below!

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