Single point of failure identification in HLD - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to identify the component that can cause a system outage if it fails.

HLD

if system.has_single_[1]():
    alert('Single point of failure detected')

Drag options to blanks, or click blank then click option'

Anode

Bredundancy

Cbackup

Dreplica

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing redundancy with the failing component.

The term 'node' refers to a single component in the system. If there is only one node performing a critical task, it is a single point of failure.

2fill in blank

medium

Complete the code to check if the database is a single point of failure.

HLD

if database.[1] == 1:
    print('Warning: Single point of failure in database')

Drag options to blanks, or click blank then click option'

Aqueries

Breplicas

Cusers

Dconnections

Attempts:

3 left

💡 Hint

Common Mistakes

Checking connections or users instead of replicas.

If the database has only one replica, it means no backup exists, making it a single point of failure.

3fill in blank

hard

Fix the error in the code that identifies a single point of failure in the load balancer.

HLD

if load_balancer.status == '[1]':
    raise Exception('Single point of failure detected')

Drag options to blanks, or click blank then click option'

Afailed

Binactive

Credundant

Dactive

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'inactive' or 'active' which do not indicate failure.

The load balancer failing ('failed' status) indicates a single point of failure if no backup exists.

4fill in blank

hard

Fill both blanks to detect single points of failure in a system with multiple components.

HLD

for component in system.components:
    if component.is_[1]() and not component.has_[2]():
        print(f'Single point of failure: {component.name}')

Drag options to blanks, or click blank then click option'

Acritical

Bbackup

Credundancy

Doptional

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing backup with redundancy or optional with critical.

A component is a single point of failure if it is critical and lacks redundancy.

5fill in blank

hard

Fill all three blanks to complete the function that identifies single points of failure in a distributed system.

HLD

def identify_spof(nodes):
    spof_nodes = [node for node in nodes if node.is_[1]() and node.has_no_[2]() and node.depends_on_[3]()]
    return spof_nodes

Drag options to blanks, or click blank then click option'

Acritical

Bredundancy

Csingle_node

Dbackup

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing backup and redundancy or misunderstanding dependencies.

The function finds nodes that are critical, have no redundancy, and depend on a single node, marking them as single points of failure.

Practice

1. Which component in a system is called a single point of failure?

easy

A. A part that never fails

B. A component that has multiple backups

C. A part that, if it fails, stops the whole system from working

D. A component that only handles logging

Solution

1. Step 1: Understand the definition of single point of failure

   A single point of failure is a part of the system that can cause the entire system to stop working if it breaks.

2. Step 2: Match the definition to the options

   A part that, if it fails, stops the whole system from working describes a component that stops the whole system if it fails, which matches the definition.

3. Final Answer:

   A part that, if it fails, stops the whole system from working -> Option C

4. Quick Check:

   Single point of failure = component causing total failure [OK]

Hint: Look for the component whose failure stops everything [OK]

Common Mistakes:

• Confusing components with backups as single points of failure
• Thinking a component that never fails is a single point of failure
• Assuming logging components cause total failure

2. Which of the following is the correct way to reduce a single point of failure in a database server?

easy

A. Disable backups to improve speed

B. Use a single database server with no backups

C. Store all data on a local hard drive only

D. Add a replica database server for failover

Solution

1. Step 1: Identify how to reduce single points of failure

   Reducing single points of failure means adding backups or alternatives to critical components.

2. Step 2: Evaluate options for database server

   Add a replica database server for failover adds a replica server, providing failover if the main server fails, reducing single point of failure.

3. Final Answer:

   Add a replica database server for failover -> Option D

4. Quick Check:

   Adding backups = reducing single point of failure [OK]

Hint: Add replicas or backups to critical components [OK]

Common Mistakes:

• Choosing single server without backups
• Ignoring failover options
• Thinking disabling backups improves reliability

3. Consider a system with a load balancer, two web servers, and replicated database servers. Which component is the single point of failure?

medium

A. Load balancer

B. Web servers

C. Database server

D. All components have backups

Solution

1. Step 1: Analyze redundancy of components

   There are two web servers and replicated database servers, so they are redundant. The load balancer is only one.

2. Step 2: Identify which component lacks backup

   The load balancer is a single device with no backup, so it is a single point of failure.

3. Final Answer:

   Load balancer -> Option A

4. Quick Check:

   Single device without backup = single point of failure [OK]

Hint: Find the component with no backup or alternative [OK]

Common Mistakes:

• Assuming web servers are single points due to multiple instances
• Ignoring load balancer as critical single device
• Thinking database servers are a single point of failure

4. A system has a single DNS server and multiple application servers. Users report downtime when DNS fails. What is the main issue?

medium

A. DNS server is a single point of failure

B. Application servers lack backups

C. Users have slow internet

D. Application servers are overloaded

Solution

1. Step 1: Understand the role of DNS server

   DNS translates domain names to IPs; if it fails, users cannot reach the system.

2. Step 2: Identify the cause of downtime

   Since downtime happens when DNS fails and there is only one DNS server, it is a single point of failure.

3. Final Answer:

   DNS server is a single point of failure -> Option A

4. Quick Check:

   Single DNS failure causes downtime = single point of failure [OK]

Hint: Check if critical service has only one instance [OK]

Common Mistakes:

• Blaming application servers without evidence
• Ignoring DNS role in connectivity
• Assuming user internet issues cause downtime

5. You design a payment system with one payment gateway, one database, and multiple app servers. Which change best removes single points of failure?

hard

A. Add more app servers only

B. Add a second payment gateway and database replica

C. Use a single faster database

D. Remove payment gateway to simplify

Solution

1. Step 1: Identify single points of failure

   Payment gateway and database each have only one instance, so they are single points of failure.

2. Step 2: Choose the best fix

   Adding a second payment gateway and a database replica adds redundancy, removing single points of failure.

3. Final Answer:

   Add a second payment gateway and database replica -> Option B

4. Quick Check:

   Adding redundancy removes single points of failure [OK]

Hint: Add backups to all critical components [OK]

Common Mistakes:

• Adding only app servers ignores gateway and database
• Using a single faster database does not add redundancy
• Removing payment gateway breaks system