1.6 Load Balancing

Question 1

What is a load balancer?

Answer 1

A server that balances incoming traffic to your application and distributes that traffic across multiple servers

Improves reliability and scalability of your application and allows replication.

Question 2

What does fault tolerance mean in the context of load balancers?

Answer 2

Enhancement of service availability by redirecting traffic away from failed or malfunctioning servers.

Question 3

What is health monitoring in load balancers?

Answer 3

Continuous monitoring of backend server health and performance, removing unresponsive servers from the pool.

Question 4

What is SSL termination?

Answer 4

Offloading SSL/TLS encryption and decryption from backend servers to improve performance.

Question 5

What is session persistence in load balancers?

Answer 5

Ensuring that subsequent requests from the same client are directed to the same backend server.

Question 6

What is geographic load balancing?

Answer 6

Distribution of traffic based on the geographical location of the client to optimize performance.

Question 7

What is content-based routing in load balancers?

Answer 7

Routing traffic based on content-specific criteria like URL paths, HTTP headers, or query parameters.

Question 8

What is Round Robin load balancing?

Answer 8

The simplest form of load balancing where each request is directed to the next server in a sequential list.

Question 9

What is the Least Connections load balancing method?

Answer 9

Routing traffic to the server with the fewest active connections.

Question 10

What does Least Response Time load balancing measure?

Answer 10

It measures the response time of each server and directs traffic to the server with the fastest response time.

Question 11

What is Source IP Hash in load balancing?

Answer 11

Requests from the same client IP address are consistently routed to the same backend server.

Question 12

What is Weighted Least Connection load balancing?

Answer 12

Similar to least connections, but servers are assigned a weight based on their capacity or performance.

Question 13

What are Application-Based Load Balancers?

Answer 13

Load balancers that operate at Layer 7 of the OSI model, allowing for advanced routing decisions.

Question 14

What are Network Load Balancers?

Answer 14

Load balancers operating at Layer 4 of the OSI model, routing traffic based on IP addresses and TCP/UDP port numbers.

Question 15

What is vertical scaling?

Answer 15

Increasing the capacity of a single server by adding more resources such as CPU, memory, or storage.

Question 16

What is horizontal scaling?

Answer 16

Adding more servers to distribute the load across multiple machines.

Question 17

Fill in the blank: Vertical scaling is also known as _______.

Answer 17

[scaling up]

Question 18

Fill in the blank: Horizontal scaling is also known as _______.

Answer 18

[scaling out]

Question 19

What is a key disadvantage of vertical scaling?

Answer 19

Limited scalability due to the maximum capacity of a single server.

Question 20

What is a key advantage of horizontal scaling?

Answer 20

High scalability by adding more servers as needed.

Question 21

What does Layer 7 load balancing operate on?

Answer 21

The Application Layer of the OSI model.

Question 22

What does Layer 4 load balancing use to direct traffic?

Answer 22

Data from network and transport layer protocols such as IP, TCP, or UDP.

Question 23

What is the role of a load balancer compared to a reverse proxy?

Answer 23

A load balancer distributes incoming network traffic across multiple servers.

Question 24

What is a reverse proxy?

Answer 24

A proxy server that retrieves resources on behalf of a client from one or more servers.

Question 25

What is a disadvantage of using a reverse proxy?

Answer 25

Can become a single point of failure if not properly configured for high availability.

Question 26

What is a key characteristic of a private IP?

Answer 26

An IP address that is reachable only between servers in the same network.

Question 27

What does database replication address?

Answer 27

Failover and redundancy issues in database design.

Question 28

What happens when a load balancer is added to a web tier?

Answer 28

Improved availability of the web tier and resolution of failover issues.

Question 31

What is the primary role of a load balancer?

Answer 31

A load balancer evenly distributes incoming traffic among web servers that are defined in a load-balanced set.

Question 32

How do users connect to a load balancer in a web application setup?

Answer 32

Users connect to the public IP of the load balancer directly. With this setup, web servers are unreachable directly by clients anymore.

Question 33

What is the purpose of using private IPs in a load-balanced setup?

Answer 33

Private IPs are used for communication between servers to enhance security. A private IP is only reachable between servers in the same network and is not accessible over the internet.

Question 34

How does a load balancer communicate with web servers in a load-balanced setup?

Answer 34

The load balancer communicates with web servers through private IPs to ensure better security and isolation.

Question 35

What happens if server 1 goes offline in a load-balanced setup?

Answer 35

If server 1 goes offline, all the traffic is routed to server 2. This prevents the website from going offline.

Question 36

What is the solution when a website’s traffic grows rapidly and two servers are not enough?

Answer 36

The load balancer can handle this issue by automatically adding more web servers to the pool. It will start sending requests to the newly added servers.

Question 37

What does the web tier setup look like after adding a load balancer and additional web servers?

Answer 37

After adding a load balancer and a second web server, the setup solves failover issues and improves the availability of the web tier, ensuring that traffic can be rerouted in case of server failure.

Question 38

What is the problem with having only one database in the current web application design?

Answer 38

Having only one database in the current design creates a single point of failure and does not support failover and redundancy.

Question 39

How can database failover and redundancy be addressed in a web application architecture?

Answer 39

Database replication is a common technique to address database failover and redundancy issues, allowing the database to be replicated across multiple servers to ensure availability.

Question 40

What is the primary function of load balancers?

Answer 40

Distributing incoming client requests to computing resources such as application servers and databases.

Question 41

List three advantages of using load balancers.

Answer 41

* Preventing requests from going to unhealthy servers * Preventing overloading resources * Helping to eliminate a single point of failure

Question 42

What are the two types of load balancers based on implementation?

Answer 42

* Hardware * Software (e.g., HAProxy)

Question 43

What does SSL termination do in the context of load balancers?

Answer 43

Decrypts incoming requests and encrypts server responses so backend servers do not have to perform these operations.

Question 44

True or False: Load balancers remove the need to install X.509 certificates on each server.

Answer 44

True

Question 45

What is session persistence in load balancers?

Answer 45

Issuing cookies and routing a specific client's requests to the same instance.

Question 46

What are the two common modes for setting up multiple load balancers?

Answer 46

* Active-passive * Active-active

Question 47

Name two metrics used by load balancers to route traffic.

Answer 47

* Random * Least loaded

Question 48

What layer do Layer 4 load balancers operate at?

Answer 48

Transport layer

Question 49

What type of information do Layer 4 load balancers look at to distribute requests?

Answer 49

Source and destination IP addresses and ports in the header.

Question 50

Fill in the blank: Layer 4 load balancers perform _______.

Answer 50

Network Address Translation (NAT)

Question 51

What layer do Layer 7 load balancers operate at?

Answer 51

Application layer

Question 52

How do Layer 7 load balancers make load-balancing decisions?

Answer 52

By looking at the contents of the header, message, and cookies.

Question 53

What is one example of a decision a Layer 7 load balancer might make?

Answer 53

Directing video traffic to servers that host videos.

Question 54

What is horizontal scaling?

Answer 54

Improving performance and availability by scaling out using commodity machines.

Question 55

List two disadvantages of horizontal scaling.

Answer 55

* Introduces complexity * Requires servers to be stateless

Question 56

What must be done with sessions when using horizontal scaling?

Answer 56

Store sessions in a centralized data store.

Question 57

What is a potential disadvantage of using a load balancer?

Answer 57

It can become a performance bottleneck if not properly resourced or configured.

Question 58

True or False: A single load balancer is not a single point of failure.

Answer 58

False

Question 59

What is one complexity introduced by configuring multiple load balancers?

Answer 59

Increased overall configuration complexity.

Question 60

What is a reverse proxy?

Answer 60

A web server that centralizes internal services and provides unified interfaces to the public

Question 61

How does a reverse proxy handle client requests?

Answer 61

Requests from clients are forwarded to a server that can fulfill it before the reverse proxy returns the server's response to the client

Question 62

List three benefits of using a reverse proxy.

Answer 62

* Increased security * Increased scalability and flexibility * SSL termination

Question 63

What is one way a reverse proxy increases security?

Answer 63

Hides information about backend servers

Question 64

What is SSL termination in the context of a reverse proxy?

Answer 64

Decrypting incoming requests and encrypting server responses so backend servers do not have to perform these operations

Question 65

Fill in the blank: A reverse proxy removes the need to install ______ on each server.

Answer 65

X.509 certificates

Question 66

What is one disadvantage of using a reverse proxy?

Answer 66

Increased complexity

Question 67

What is the difference between a load balancer and a reverse proxy?

Answer 67

Load balancers route traffic to multiple servers serving the same function, while reverse proxies can be used with just one web server

Question 68

Name two solutions that support both layer 7 reverse proxying and load balancing.

Answer 68

* NGINX * HAProxy

Question 69

What does separating the web layer from the application layer allow?

Answer 69

To scale and configure both layers independently

Question 70

What principle advocates for small and autonomous services working together?

Answer 70

Single responsibility principle

Question 71

What are microservices?

Answer 71

A suite of independently deployable, small, modular services that run a unique process and communicate through a well-defined mechanism

Question 72

Give an example of a microservice that Pinterest might use.

Answer 72

User profile

Question 73

What is service discovery?

Answer 73

A mechanism that helps services find each other by tracking registered names, addresses, and ports

Question 74

Name two systems that can be used for service discovery.

Answer 74

* Consul * Etcd

Question 75

Fill in the blank: Microservices can add ______ in terms of deployments and operations.

Answer 75

Complexity

Question 76

What is one way that workers in the application layer help enable asynchronism?

Question 77

What are health checks used for in service discovery?

Answer 77

To verify service integrity

Question 78

What is a disadvantage of adding an application layer with loosely coupled services?

Answer 78

Requires a different approach from an architectural, operations, and process viewpoint compared to a monolithic system