Why Centralized logging (ELK stack) in Microservices? - Purpose & Use Cases

The Big Idea

What if you could see all your system's problems in one place, instantly?

The Scenario

Imagine you run many small shops in different parts of a city, and each shop keeps its own paper logbook for sales and issues. When you want to check how your whole business is doing, you have to visit each shop, read through piles of papers, and try to remember what you saw. This takes a lot of time and is very tiring.

The Problem

Manually collecting logs from many services is slow and confusing. Logs are scattered everywhere, making it hard to find problems quickly. You might miss important warnings or errors because you have to look in too many places. This can cause delays in fixing issues and frustrate your team.

The Solution

The ELK stack brings all logs from different services into one place. It organizes and searches logs easily, like having a smart assistant who reads all your shop logbooks and tells you exactly what you need to know. This saves time and helps you fix problems faster.

Before vs After

✗ Before

ssh service1; cat /var/log/app.log
ssh service2; cat /var/log/app.log

✓ After

Use Filebeat to send logs to Elasticsearch and search them in the Kibana dashboard

What It Enables

With centralized logging, you can instantly see the health of all your services and quickly spot issues before customers notice.

Real Life Example

A company running many microservices uses ELK to monitor errors and performance in real time, so their support team can respond immediately to outages or slowdowns.

Key Takeaways

Manual log checking is slow and scattered.

ELK stack centralizes and organizes logs from all services.

This helps teams find and fix problems faster and keep systems healthy.

Practice

1. What is the main purpose of the ELK stack in microservices architecture?

easy

A. To manage database transactions

B. To deploy microservices automatically

C. To collect, store, and visualize logs from multiple services in one place

D. To monitor network traffic between services

Solution

1. Step 1: Understand ELK stack components

   ELK stands for Elasticsearch (storage), Logstash (processing), and Kibana (visualization), all focused on logs.

2. Step 2: Identify ELK stack role in microservices

   It centralizes logs from many services to one place for easier monitoring and troubleshooting.

3. Final Answer:

   To collect, store, and visualize logs from multiple services in one place -> Option C

4. Quick Check:

   ELK stack = centralized logging [OK]

Hint: ELK = Elasticsearch + Logstash + Kibana for logs [OK]

Common Mistakes:

• Confusing ELK with deployment tools
• Thinking ELK manages databases
• Assuming ELK monitors network traffic

2. Which of the following is the correct Docker Compose service name for running Elasticsearch in an ELK stack?

easy

A. elasticsearch

B. kibana

C. logstash

D. filebeat

Solution

1. Step 1: Recall ELK stack components

   Elasticsearch stores logs, Logstash processes, Kibana visualizes, Filebeat ships logs.

2. Step 2: Identify correct service name in Docker Compose

   The service running Elasticsearch is named "elasticsearch" in Docker Compose files.

3. Final Answer:

   elasticsearch -> Option A

4. Quick Check:

   Elasticsearch service = elasticsearch [OK]

Hint: Elasticsearch service is named 'elasticsearch' in Docker Compose [OK]

Common Mistakes:

• Confusing Logstash or Kibana as Elasticsearch service
• Using 'filebeat' as ELK core service
• Misspelling service names

3. Given this Logstash configuration snippet:

input { beats { port => 5044 } } output { elasticsearch { hosts => ["http://elasticsearch:9200"] } }

What happens when Logstash receives logs on port 5044?

medium

A. Logs are discarded because port 5044 is incorrect

B. Logs are sent to Elasticsearch at http://elasticsearch:9200

C. Logs are visualized directly by Kibana

D. Logs are stored locally on Logstash server

Solution

1. Step 1: Analyze Logstash input configuration

   Logstash listens for logs from Beats agents on port 5044.

2. Step 2: Analyze Logstash output configuration

   Logs received are forwarded to Elasticsearch at the specified host and port.

3. Final Answer:

   Logs are sent to Elasticsearch at http://elasticsearch:9200 -> Option B

4. Quick Check:

   Logstash input port 5044 forwards logs to Elasticsearch [OK]

Hint: Logstash input port 5044 sends logs to Elasticsearch host [OK]

Common Mistakes:

• Assuming logs go directly to Kibana
• Thinking port 5044 is invalid
• Believing logs are stored locally on Logstash

4. You configured Logstash to receive logs on port 5044, but no logs appear in Elasticsearch. Which is the most likely cause?

medium

A. Docker Compose file is missing Kibana service

B. Kibana is not running

C. Logstash input port is set to 9200 instead of 5044

D. Elasticsearch service is down or unreachable

Solution

1. Step 1: Check connectivity between Logstash and Elasticsearch

   If Elasticsearch is down or unreachable, Logstash cannot send logs to it.

2. Step 2: Verify other options

   Kibana not running or missing does not stop logs from reaching Elasticsearch; wrong input port would prevent Logstash from receiving logs, not sending.

3. Final Answer:

   Elasticsearch service is down or unreachable -> Option D

4. Quick Check:

   Logs missing usually means Elasticsearch unreachable [OK]

Hint: Check Elasticsearch status if logs don't appear [OK]

Common Mistakes:

• Blaming Kibana for missing logs in Elasticsearch
• Confusing input port with Elasticsearch port
• Ignoring Elasticsearch service health

5. You want to add a new microservice that sends logs to the ELK stack using Filebeat. Which steps should you take to ensure logs appear in Kibana?

hard

A. Install Filebeat on the microservice host, configure it to send logs to Logstash on port 5044, and verify Elasticsearch and Kibana are running

B. Install Kibana on the microservice host and configure it to collect logs directly

C. Configure Elasticsearch to pull logs from the microservice host automatically

D. Run Logstash on the microservice host and send logs directly to Kibana

Solution

1. Step 1: Setup Filebeat on microservice host

   Filebeat collects logs locally and forwards them to Logstash on port 5044.

2. Step 2: Ensure ELK stack components are running

   Logstash processes logs, sends them to Elasticsearch, and Kibana visualizes them.

3. Final Answer:

   Install Filebeat on the microservice host, configure it to send logs to Logstash on port 5044, and verify Elasticsearch and Kibana are running -> Option A

4. Quick Check:

   Filebeat -> Logstash -> Elasticsearch -> Kibana [OK]

Hint: Filebeat sends logs to Logstash; Kibana visualizes them [OK]

Common Mistakes:

• Trying to send logs directly to Kibana
• Expecting Elasticsearch to pull logs automatically
• Running Logstash on microservice host unnecessarily