**Haproxy interview questions and answers**

Table of Contents

1) Is HAProxy a load balancer?

HAProxy (High Availability Proxy) is open source proxy and load balancing server software. It provides high availability at the network (TCP) and application (HTTP/S) layers, improving speed and performance by distributing workload across multiple servers.

2)What are the different types of load balancers?

Elastic Load Balancing supports the following types of load balancers: Application Load Balancers, Network Load Balancers, and Classic Load Balancers.

3) What is difference between ELB and ALB?

An ALB can tie instances to different groups of servers, called target groups, and configure routing. Unlike ELBs, which are directly instantiated, services can be run independently and multiple routing rule definitions can be created.

4) What is API data?

API is an acronym for Application Programming Interface that software uses to access data, server software or other applications and have been around for quite some time. In layman’s terms, it is a software intermediary that allows two applications to talk to each other.

5) What is REST web?

Representational State Transfer (REST) is an architectural style that specifies constraints, such as the uniform interface, that if applied to a web service induce desirable properties, such as performance, scalability, and modifiability, that enable services to work best on the Web.

6) What is SDK programming?

SDK stands for software development kit. Also known as a devkit, the SDK is a set of software-building tools for a specific platform, including the building blocks, debuggers and, often, a framework or group of code libraries such as a set of routines specific to an operating system (OS).

7) Where is HAProxy setup?

All settings are defined in the file /etc/haproxy/haproxy. cfg (or /etc/hapee-{version}/hapee-lb. cfg for HAProxy Enterprise). If you are using Docker, then this file is mounted as a volume into the container at the path /usr/local/etc/haproxy/haproxy.

8) What is HAProxy frontend?

When HAProxy Enterprise is used as a reverse proxy in front of your backend servers, a frontend section defines the IP addresses and ports that clients can connect to. You may add as many frontend sections as needed to expose various websites or applications to the Internet.

9) What port does HAProxy use?

port 80
HAProxy forwards the request to the server port referenced in its configuration file (generally port 80).

10) What is L4 and L7 load balancing?

L4 load balancing delivers traffic with limited network information with a load balancing algorithm (i.e. round-robin) and by calculating the best server based on fewest connections and fastest server response times. L7 load balancing works at the highest level of the OSI model.

11) How does ALB route traffic?

A load balancer accepts incoming traffic from clients and routes requests to its registered targets (such as EC2 instances) in one or more Availability Zones. The load balancer also monitors the health of its registered targets and ensures that it routes traffic only to healthy targets.

12) Why REST is called stateless?

As per the REST architecture, a RESTful Web Service should not keep a client state on the server. This restriction is called Statelessness. It is the responsibility of the client to pass its context to the server and then the server can store this context to process the client’s further request.

13) What are REST principles?

REST principles are defined by four interface controls, including identifying resources, managing resources through representations, self-descriptive communications, and hypermedia as the engine of the application state.

14) Why is API needed?

APIs are needed to bring applications together in order to perform a designed function built around sharing data and executing pre-defined processes. They work as the middle man, allowing developers to build new programmatic interactions between the various applications people and businesses use on a daily basis.

15) What is listen in HAProxy?

A listen section can be used to define a complete proxy with the functions of a frontend and backend combined. The listen section is well suited whenever you need to route traffic to a specific set of servers or for non-HTTP-related configurations such as TCP gateways.

16) Is HAProxy a forward proxy?

So basically, because HAProxy is not a forward proxy, it will not actually…it will, by default, just pass my request like it is now, like with all that big path that we want.

17) What is HAProxy enterprise?

HAProxy Enterprise is the industry’s leading software load balancer. It powers modern application delivery at any scale and in any environment, providing the utmost performance, observability and security.

18) What is HAProxy configuration?

There are four essential sections to an HAProxy configuration file. They are global , defaults , frontend , and backend . These four sections define how the server as a whole performs, what your default settings are, and how client requests are received and routed to your backend servers.

19) How many connections can HAProxy handle?

In HAProxy, you can add more servers to handle more concurrent connections. In this example, HAProxy allows 30 active connections per server. If all of the servers are maxed out, connections queue up, waiting for an available server.

20) What is Edge proxy?

An edge proxy server is a proxy server that is positioned on the edge of an intranet and connects to an origin server through the Internet. An edge proxy server is not bound to any other proxy server.

21) What is layered system in REST?

Layered system

REST allows you to use a layered system architecture where you deploy the APIs on server A, and store data on server B and authenticate requests in Server C, for example. A client cannot ordinarily tell whether it is connected directly to the end server or an intermediary along the way.

22) How do I set timeout in HAProxy?

Timeout Client. The setting defines the maximum time a client can be inactive when connected to the server. A common value for this timeout is five minutes. …
Timeout Connect. The works like a grace period. …
Timeout Server. When a client sends a request to the server, it expects a response

23) How use HAProxy reverse proxy?

Steps to configure HAProxy
Step 1 – Install HAProxy. …
Step 2 – Copy the configuration file for the reverse proxy. …
Step 3 – Change frontend port and assign backend IPs. …
Step 4 – Copy haproxy.cfg to the managed node. …
Step 5 – Start the service.

24) Is HAProxy stateful?

The operations are always stateful, and the return traffic must pass through the load balancer.

25) How do I view HAProxy logs?

When you are troubleshooting HAProxy using its log file, examine /var/log/haproxy. log for errors using a tool like tail or less . For example, to view the last two lines of the log using tail , run the following command: sudo tail -n 2 /var/log/haproxy.

26) How does nginx reverse proxy work?

Nginx reverse proxy acts as an intermediate server that intercepts client requests and forwards them to the appropriate upstream backend server and subsequently forwarded a response from the server back to the client. The reverse proxy provides various benefits as an abstract layer above upstream servers.

27) Does HAProxy terminate connection?

HAProxy only uses valid servers. Other ones are automatically evicted from load balancing farms under certain conditions it is still possible to force to use. It also supports a graceful shutdown so that it is possible to take servers out of a farm without affecting any connection.

28) What is a transparent proxy?

A transparent proxy, also known as an inline proxy, intercepting proxy or forced proxy, is a server that intercepts the connection between an end-user or device and the internet. It is called “transparent” because it does so without modifying requests and responses.

29) How do you know if HAProxy is running?

Now examine HAProxy’s status and make sure that the output shows an active (running) line: sudo systemctl status haproxy. service.

30) What is upstream and downstream in NGINX?

According to this definition: if you are looking at a request, then the client is upstream, and the server is downstream; in contrast, if you are looking at a response, then the client is downstream, and the server is upstream.

31) What is Proxy_add_x_forwarded_for?

The $proxy_add_x_forwarded_for is equal to $http_x_forwarded_for,$remote_addr , and the $remote_addr variable will be changed when http_realip_module is used. So you will not get the last proxy addr in that header. Changing the order of directives won’t have an effect because nginx configuration is declarative.

32) Does HAProxy use OpenSSL?

HAProxy is compiled with OpenSSL, which allows it to encrypt and decrypt traffic as it passes.

33) How many connections can HAProxy handle?

34) Does HAProxy reuse connections?

So use it if your servers and environment allow it! Safe and aggressive modes have good results when the client can keep the connection persistent for several requests. The longer the distance between HAProxy and the server, the more benefit the reuse feature will bring to your global application response time.

35) What DNS transparent?

A transparent DNS proxy is the practice of intercepting DNS requests destined for a specific recursive DNS server (like DNSFilter), and sending the DNS requests to a completely different DNS server.

36) How do you stop HAProxy?

HAProxy supports a graceful and a hard stop. The hard stop is simple, when the SIGTERM signal is sent to the haproxy process, it immediately quits and all established connections are closed. The graceful stop is triggered when the SIGUSR1 signal is sent to the haproxy process.

37) What is HAProxy health check?

HAProxy provides active, passive, and agent health checks. HAProxy makes your web applications highly available by spreading requests across a pool of backend servers. … Without health checks, HAProxy has no way of knowing when a server has become dysfunctional.

38) What is Proxy_redirect?

Nginx proxy_redirect: Change response-header Location and Refresh in the response of the server.

39) What is Proxy_buffering?

proxy_buffering on; Context: http , server , location. Enables or disables buffering of responses from the proxied server. When buffering is enabled, nginx receives a response from the proxied server as soon as possible, saving it into the buffers set by the proxy_buffer_size and proxy_buffers directives.

40) What is Http_x_forwarded_for?

HTTP_X_FORWARDED_FOR is often used to detect the client IP address, but without any additional checks, this can lead to security issues, especially when this IP is later used for authentication or in SQL queries without sanitization.

41) Is HAProxy a reverse proxy?

HAProxy is a reverse proxy that sits in front of the two web servers and routes requests to them.

42) Is HAProxy multithreaded?

In the multithreading model, HAProxy starts multiple threads within a single process rather than starting multiple individual processes, and as such, it avoids all of the aforementioned problems. Multithreading support has been implemented and included in HAProxy starting with HAProxy 1.8.

43) What is HAProxy and Keepalived?

HAProxy (High Availability Proxy) is a free, very fast and reliable solution offering high availability, load balancing, and proxying for TCP and HTTP-based applications. On the other hand, Keepalived is detailed as “A routing software written in C”.

44) Is my internet going through a proxy?

Click the “Connections” tab in the Internet Options window. Click the “LAN Settings” button. If there is a check mark in the box next to the “Us a proxy server for your LAN” option, then your PC accesses the Web through a proxy server. If there is no check mark in the box, your computer does not use a proxy server.

45) What is Proxy_send_timeout?

proxy_send_timeout Sets a timeout for transmitting a request to the proxied server. The timeout is set only between two successive write operations, not for the transmission of the whole request. If the proxied server does not receive anything within this time, the connection is closed.

46) What is chain proxy?

Proxy chaining involves forwarding traffic from one proxy server to another. This method leverages your existing proxy servers, with no additional changes to the network. It’s a quick and easy way to forward your traffic to the Zscaler service from an existing on-premises proxy.

47) What does client IP mean?

Client IP means any Intellectual Property Rights owned or licensed by the Client; Sample 2. Sample 3. Based on 8 documents 8. Client IP means proprietary systems, software, information, logos, services names, domain names, marks and copyrights the Client uses.

48) Is HAProxy secure?

The HAProxy Guide to Multilayered Security

HAProxy gives you the building blocks to create a strong, layered defense against DDoS, malicious bot traffic, vulnerability scanners and more. Using its flexible configuration language, you’ll learn to: Protect your services from application-layer DDoS attacks.

49) What is frontend and backend in HAProxy?

50)Troubleshooting with haproxy

To troubleshoot HAProxy configuration issues, use the haproxy -c command. The tool will parse your HAProxy files and detect any errors or missing settings before attempting to start the server. Run the command like this on Ubuntu, Debian, CentOS, and Fedora based distributions.

51) Am I using a VPN or proxy?

To see if you’re using a proxy/VPN online, go to www.whatismyproxy.com. It will say if you’re connected to a proxy or not. PC: Check under your WiFi settings, to see if there is a VPN/proxy showing up.

52) What is an open proxy IP address?

An open proxy is a type of proxy server that is accessible by any Internet user. Generally, a proxy server only allows users within a network group (i.e. a closed proxy) to store and forward Internet services such as DNS or web pages to reduce and control the bandwidth used by the group.