Liveness and readiness probes in Microservices - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a liveness probe in microservices?

A liveness probe checks if a service is alive and running. If it fails, the system restarts the service to fix it.

beginner

What does a readiness probe do?

A readiness probe checks if a service is ready to accept traffic. If it fails, the service is removed from load balancing until ready.

intermediate

Why use both liveness and readiness probes together?

Using both helps keep services healthy and only sends traffic to services that are ready, improving reliability and user experience.

beginner

Give a simple example of a liveness probe check.

A liveness probe might send an HTTP GET request to "/healthz" endpoint. If it returns 200 OK, the service is alive.

intermediate

What happens if a readiness probe fails continuously?

The service stops receiving new requests but keeps running. This prevents sending traffic to a service that can't handle it yet.

What is the main purpose of a liveness probe?

A To balance load between services

B To check if the service is alive and restart if needed

C To monitor network latency

D To check if the service is ready to accept traffic

Liveness probes detect if a service is alive and restart it if it is not responding.

If a readiness probe fails, what happens?

A The service is removed from load balancer and stops receiving traffic

B The service is restarted immediately

C The service shuts down

D Nothing happens

Readiness probe failure means the service is not ready, so it stops receiving new traffic but keeps running.

Which probe helps avoid sending traffic to a service that is not ready?

A Liveness probe

B Load balancer

C Startup probe

D Readiness probe

Readiness probes ensure traffic is only sent to services ready to handle requests.

What is a common method used by liveness probes to check service health?

A Measuring disk space

B Checking CPU usage

C Sending an HTTP GET request to a health endpoint

D Verifying user login

Liveness probes often use HTTP GET requests to a health check endpoint to verify service health.

Why is it important to have both liveness and readiness probes?

A To restart services and manage traffic properly

B To increase CPU usage

C To reduce network bandwidth

D To log user activity

Both probes together help keep services running and only send traffic when services are ready.

Explain the difference between liveness and readiness probes in microservices.

Think about when a service should be restarted versus when it should just stop receiving traffic.

Describe a real-life scenario where readiness probes improve user experience.

Imagine a restaurant kitchen not ready to serve but still open.

Practice

1. What is the main purpose of a liveness probe in microservices?

easy

A. To check if the service is ready to accept traffic

B. To log user requests for debugging

C. To monitor the network latency between services

D. To check if the service is alive and restart it if it is not

Solution

1. Step 1: Understand the role of liveness probes

   Liveness probes detect if a service is stuck or dead and need restarting.

2. Step 2: Differentiate from readiness probes

   Readiness probes check if the service can handle requests, not if it is alive.

3. Final Answer:

   To check if the service is alive and restart it if it is not -> Option D

4. Quick Check:

   Liveness probe = check alive and restart [OK]

Hint: Liveness = alive and restart, Readiness = ready for traffic [OK]

Common Mistakes:

• Confusing liveness with readiness probes
• Thinking liveness probes check traffic readiness
• Assuming liveness probes monitor performance

2. Which of the following is the correct syntax to define a readiness probe in a Kubernetes pod spec?

easy

A. livenessProbe:
exec:
command: ["cat", "/tmp/healthy"]
timeoutSeconds: 1

B. livenessProbe:
tcpSocket:
port: 8080
initialDelaySeconds: 5
periodSeconds: 10

C. readinessProbe:
httpGet:
path: /healthz
port: 8080
initialDelaySeconds: 5
periodSeconds: 10

D. livenessProbe:
httpGet:
path: /ready
port: 8080
failureThreshold: 3

Solution

1. Step 1: Identify readiness probe syntax

   Readiness probes often use httpGet with path and port, plus delay and period settings.

2. Step 2: Confirm correct fields and indentation

   readinessProbe: httpGet: path: /healthz port: 8080 initialDelaySeconds: 5 periodSeconds: 10 correctly shows readinessProbe with httpGet, initialDelaySeconds, and periodSeconds.

3. Final Answer:

   readinessProbe: httpGet: path: /healthz port: 8080 initialDelaySeconds: 5 periodSeconds: 10 -> Option C

4. Quick Check:

   Readiness probe syntax = readinessProbe: httpGet: path: /healthz port: 8080 initialDelaySeconds: 5 periodSeconds: 10 [OK]

Hint: Readiness uses httpGet with path and port in YAML [OK]

Common Mistakes:

• Mixing livenessProbe and readinessProbe fields
• Incorrect indentation in YAML
• Using wrong probe type for readiness

3. Given this Kubernetes pod spec snippet, what will happen if the readiness probe fails continuously?

readinessProbe:
  httpGet:
    path: /ready
    port: 8080
  initialDelaySeconds: 5
  periodSeconds: 10
  failureThreshold: 3

medium

A. The pod will be restarted immediately

B. The pod will be marked as not ready and removed from service endpoints

C. The pod will ignore the failure and continue serving traffic

D. The pod will scale up automatically

Solution

1. Step 1: Understand readiness probe failure effect

   Readiness probe failure marks pod as not ready, so it stops receiving traffic.

2. Step 2: Differentiate from liveness probe effect

   Liveness probe failure triggers pod restart, readiness does not.

3. Final Answer:

   The pod will be marked as not ready and removed from service endpoints -> Option B

4. Quick Check:

   Readiness failure = pod not ready, no restart [OK]

Hint: Readiness failure removes pod from load balancer, no restart [OK]

Common Mistakes:

• Confusing readiness failure with pod restart
• Assuming pod scales automatically on probe failure
• Ignoring failureThreshold effect

4. A microservice has a liveness probe configured as an HTTP GET on /health. The service sometimes returns HTTP 500 during startup but is healthy afterward. What is the best fix to avoid unnecessary restarts?

medium

A. Increase initialDelaySeconds to allow startup time before probing

B. Change the probe to readiness probe instead of liveness probe

C. Remove the probe completely to avoid restarts

D. Set failureThreshold to 1 to detect failures faster

Solution

1. Step 1: Identify cause of restarts

   Liveness probe fails during startup because service returns HTTP 500 before ready.

2. Step 2: Adjust probe timing to avoid false failures

   Increasing initialDelaySeconds delays probe start, allowing service to become healthy first.

3. Final Answer:

   Increase initialDelaySeconds to allow startup time before probing -> Option A

4. Quick Check:

   Delay liveness probe start to avoid false failures [OK]

Hint: Delay liveness probe start to avoid false failure during startup [OK]

Common Mistakes:

• Removing probes which reduces reliability
• Confusing readiness and liveness probe roles
• Setting failureThreshold too low causing quick restarts

5. You have a microservice that takes time to initialize resources before it can serve requests. You want to ensure it is not restarted unnecessarily but also not receive traffic before ready. How should you configure liveness and readiness probes?

hard

A. Set liveness probe with a longer initialDelaySeconds and readiness probe to check resource initialization

B. Use only a liveness probe with a short periodSeconds to restart fast

C. Use only a readiness probe and no liveness probe

D. Set both probes to the same HTTP path and timing

Solution

1. Step 1: Prevent unnecessary restarts during initialization

   Set liveness probe initialDelaySeconds long enough to avoid restarting while initializing.

2. Step 2: Use readiness probe to block traffic until ready

   Readiness probe should check if resources are initialized before accepting traffic.

3. Final Answer:

   Set liveness probe with a longer initialDelaySeconds and readiness probe to check resource initialization -> Option A

4. Quick Check:

   Liveness delay + readiness check = safe startup [OK]

Hint: Delay liveness, readiness blocks traffic until ready [OK]

Common Mistakes:

• Using only one probe type causing traffic or restart issues
• Setting same path and timing for both probes
• Not delaying liveness probe causing premature restarts