TCP probe configuration in Kubernetes - Mini Project: Build & Apply

TCP Probe Configuration in Kubernetes

📖 Scenario: You are managing a Kubernetes deployment for a simple web application. To ensure your application is healthy and ready to serve traffic, you need to configure a TCP readiness probe. This probe will check if the application is accepting TCP connections on a specific port.

🎯 Goal: Configure a Kubernetes pod manifest with a TCP readiness probe on port 80. This probe will help Kubernetes know when the pod is ready to receive traffic.

📋 What You'll Learn

Create a pod manifest named tcp-probe-pod.yaml with a container named webapp.

Set the container image to nginx:latest.

Add a readiness probe using TCP socket on port 80.

Set initialDelaySeconds to 5 and periodSeconds to 10 for the readiness probe.

💡 Why This Matters

🌍 Real World

TCP probes are used in Kubernetes to check if an application is ready to accept network connections, which is important for load balancing and service availability.

💼 Career

Understanding how to configure readiness and liveness probes is essential for DevOps engineers and site reliability engineers to maintain healthy Kubernetes applications.

1

Create the basic pod manifest

Create a YAML file named tcp-probe-pod.yaml with a pod named tcp-probe-pod that has one container named webapp using the image nginx:latest. Include the apiVersion, kind, and metadata fields.

Kubernetes

# Your code here

Hint

Start with the basic pod structure and specify the container details.

2

Add the readiness probe configuration

Add a readinessProbe section under the container webapp. Configure it to use a TCP socket on port 80.

Kubernetes

apiVersion: v1
kind: Pod
metadata:
  name: tcp-probe-pod
spec:
  containers:
  - name: webapp
    image: nginx:latest
    # Add readinessProbe with tcpSocket on port 80

Hint

Use tcpSocket under readinessProbe and specify the port number.

3

Add timing settings to the readiness probe

Add initialDelaySeconds set to 5 and periodSeconds set to 10 inside the readinessProbe configuration under the container webapp.

Kubernetes

apiVersion: v1
kind: Pod
metadata:
  name: tcp-probe-pod
spec:
  containers:
  - name: webapp
    image: nginx:latest
    readinessProbe:
      tcpSocket:
        port: 80
      # Add initialDelaySeconds: 5 and periodSeconds: 10 here

Hint

Place these timing settings at the same level as tcpSocket inside readinessProbe.

4

Display the final pod manifest

Print the complete content of the tcp-probe-pod.yaml file to verify the readiness probe configuration.

Kubernetes

# Print the pod manifest content
# Your code here

Hint

Use multiple print statements to output each line of the YAML manifest exactly as shown.

Practice

1. What is the main purpose of a TCP probe in Kubernetes?

easy

A. To check the container's memory usage

B. To monitor CPU usage of a container

C. To verify the container's file system integrity

D. To check if a container accepts TCP connections on a specified port

Solution

1. Step 1: Understand TCP probe function

   A TCP probe tests if a container is accepting TCP connections on a specific port.

2. Step 2: Compare with other options

   CPU, memory, and file system checks are not done by TCP probes but by other mechanisms.

3. Final Answer:

   To check if a container accepts TCP connections on a specified port -> Option D

4. Quick Check:

   TCP probe = connection check [OK]

Hint: TCP probe checks port connectivity, not resource usage [OK]

Common Mistakes:

• Confusing TCP probe with CPU or memory monitoring
• Thinking TCP probe checks file system health
• Assuming TCP probe checks HTTP endpoints

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

easy

A. livenessProbe:
tcpSocket:
path: "/health"
initialDelaySeconds: 5
periodSeconds: 10

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

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

D. livenessProbe:
exec:
command: ["curl", "localhost:8080"]
initialDelaySeconds: 5
periodSeconds: 10

Solution

1. Step 1: Identify TCP probe syntax

   TCP probes use tcpSocket with a port field, no path.

2. Step 2: Check options for correctness

   livenessProbe: tcpSocket: port: 8080 initialDelaySeconds: 5 periodSeconds: 10 uses tcpSocket with port 8080 and timing fields correctly. Others use HTTP or exec or invalid fields.

3. Final Answer:

   livenessProbe with tcpSocket and port field -> Option C

4. Quick Check:

   TCP probe syntax = tcpSocket + port [OK]

Hint: TCP probes use tcpSocket with port, no path [OK]

Common Mistakes:

• Using httpGet or exec instead of tcpSocket for TCP probes
• Adding a path field to tcpSocket (invalid)
• Omitting port number in tcpSocket

3. Given this pod spec snippet, what will happen if the container does not accept TCP connections on port 3306?

livenessProbe:
  tcpSocket:
    port: 3306
  initialDelaySeconds: 10
  periodSeconds: 5

medium

A. Kubernetes will ignore the failure and keep the container running

B. Kubernetes will restart the container after the probe fails

C. The container will be marked ready immediately

D. The pod will be deleted permanently

Solution

1. Step 1: Understand liveness probe behavior

   Liveness probes check if a container is alive; failure triggers a restart.

2. Step 2: Apply to TCP probe failure

   If TCP connection on port 3306 fails, Kubernetes restarts the container to fix it.

3. Final Answer:

   Kubernetes will restart the container after the probe fails -> Option B

4. Quick Check:

   Liveness probe failure = container restart [OK]

Hint: Liveness probe failure triggers container restart [OK]

Common Mistakes:

• Confusing liveness with readiness probe effects
• Thinking pod is deleted permanently on failure
• Assuming failure is ignored

4. You configured a TCP readiness probe but Kubernetes reports probe failures immediately after pod start. Which is the most likely cause?

medium

A. initialDelaySeconds is missing or too low, so probe runs before container is ready

B. tcpSocket port is set to 0, which is invalid

C. periodSeconds is set too high, causing delayed checks

D. readinessProbe cannot use tcpSocket, only httpGet

Solution

1. Step 1: Analyze probe timing parameters

   Without initialDelaySeconds, probe starts immediately, possibly before container is ready.

2. Step 2: Evaluate other options

   Port 0 is invalid but would cause different errors; periodSeconds affects frequency, not immediate failure; tcpSocket is valid for readiness probes.

3. Final Answer:

   initialDelaySeconds is missing or too low, so probe runs before container is ready -> Option A

4. Quick Check:

   Missing initialDelaySeconds = early probe failure [OK]

Hint: Set initialDelaySeconds to delay probe start [OK]

Common Mistakes:

• Assuming tcpSocket is invalid for readiness probes
• Ignoring initialDelaySeconds importance
• Confusing periodSeconds with initialDelaySeconds

5. You want to configure a TCP readiness probe for a database container on port 5432. The container takes about 20 seconds to start accepting connections. Which configuration is best to avoid false failures?

hard

A. readinessProbe:
tcpSocket:
port: 5432
initialDelaySeconds: 25
periodSeconds: 10
failureThreshold: 3

B. readinessProbe:
tcpSocket:
port: 5432
initialDelaySeconds: 5
periodSeconds: 5
failureThreshold: 1

C. readinessProbe:
tcpSocket:
port: 5432
initialDelaySeconds: 0
periodSeconds: 10
failureThreshold: 5

D. readinessProbe:
tcpSocket:
port: 5432
initialDelaySeconds: 10
periodSeconds: 20
failureThreshold: 1

Solution

1. Step 1: Match initialDelaySeconds to container startup time

   Container needs ~20 seconds to accept connections, so initialDelaySeconds should be at least 20 to avoid early failures.

2. Step 2: Use periodSeconds and failureThreshold to allow retries

   Period of 10 seconds and failureThreshold of 3 means Kubernetes retries for up to 30 seconds before marking not ready, avoiding false negatives.

3. Final Answer:

   readinessProbe with initialDelaySeconds 25, periodSeconds 10, failureThreshold 3 -> Option A

4. Quick Check:

   Delay + retries prevent false failures [OK]

Hint: Set initialDelaySeconds > startup time, use retries [OK]

Common Mistakes:

• Setting initialDelaySeconds too low causing false failures
• Using failureThreshold of 1 with short delays
• Ignoring container startup time in probe config