SRE Interview Questions

SRE(Site Reliability Engineer) Interview Questions and Answers for Experienced

21) Define the Error budget policy.

An error budget policy explains how a business makes decisions to trade off reliable work instead of another featured work when SLO indicates a service is not reliable enough.

22) What are Error Budgets? And for what error budgets are used?

Error budget describes the time a technical system can collapse without prescribed effects.

Error budget motivates the teams to minimize actual incidents and maximize innovation by taking risks within acceptable limits.

23) How do you calculate budget errors in SRE?

An error budget is one minus the SLO of the service. A 99.9% SLO service has a 0.1% error budget. If our service receives 1,000,000 requests in four weeks, a 99.9% availability SLO gives us a budget of 1,000 errors over that period.

24) Explain the fundamental difference between atime, mtime, and time.

• atime described when someone accessed a file for the last time. For example, if you opened the file to view it.
• mtime tells when someone has modified a file for the last time. For example- someone has changed some of the texts in the file if it's a text(.txt) file.
• time tells when the inode contents of a file were changed, for instance, the mode or owner.
   

25) What is the fundamental difference between a process and a thread?

A thread is also a kind of process. But it is a lightweight process. Each process has a distinct heap, text, data, and stack. Threads have their stack but share data, heap, and text with the process. Text is the actual set of instructions; data is the input to the program, and the heap is the memory that stores files, locks, and sockets.
 

26) Explain Data Structure. Name some data structures.

The data structure is a framework for organizing, managing, and storing data, making it easy to access and modify. A data structure is a grouping of data values with the connections between them and the functions or operations that may be performed on the data.

Here is a list of various data structure types:

Linear: Arrays, lists

Tree: Binary, heaps

Graphs: Decision, Acyclic, etc

Hash: Distributed hash table, hash tree, etc

27) How character device and a block device are distinguished from each other?

Block devices are generally buffered and read/written in fixed sizes, such as hard drives and cd-roms. Characters' devices read/write one character at a time, such as from a keyboard or a tty, and are not buffered.

28) What is a zombie process?

A zombie process is a type of process that has completed execution. But still, its entry is present in the process table that allows the parent to read the child's exit status. The process became a zombie since its parent hasn't "reaped" it yet, even though it is "dead."

To read the child's exit status, parent processes often send the wait system call. After which the zombie is eliminated.

The zombie process is not affected by the kill command. A SIGCHLD signal is sent to the parent after a child passes away. Except the minimal amount of space they occupy when they appear in the process id table, zombie processes do not consume any system resources.

29) What is proc in file system?

In a Linux-based operating system, /proc is a special virtual filesystem that provides an interface to kernel data structures and system information. It doesn't contain regular files but rather exposes information about processes, system resources, hardware configuration, and more in a hierarchical structure. It allows users and processes to read and sometimes write to kernel data structures, providing insight into the system's state and enabling system monitoring and debugging.

30) What is DHCP, and for what is it used?

A DHCP server assigns each device in the network a dynamic IP address. Other network configuration parameters to communicate with other IP networks. DHCP is a network management protocol used on Internet Protocol (IP) networks.

Few used DHCP servers are as follows:

Automatically asking the Internet service provider for IP addresses and networking parameters (ISP)

Reducing the need for a network administrator or user to assign IP addresses to all network devices manually.

31) What are the Linux kill commands? Enlist all the Linux kill commands with their functions

In Linux, the kill command is used to terminate processes. Here are some common variations of the kill command:

• kill - Sends a signal to a process. By default, it sends the SIGTERM signal, which is a graceful termination request.
• kill -9 or kill -SIGKILL - Sends the SIGKILL signal to a process, forcing it to terminate immediately. This signal cannot be caught or ignored by the process.
• killall - Terminates all processes with the specified name. It's useful when multiple instances of a process need to be stopped.
• pkill - Terminates processes based on criteria such as process name, user, group, or other attributes.              

32) How do you apply OOPs principles in server design?

Applying Object-Oriented Programming (OOP) principles in server design involves structuring the codebase around objects and classes to promote modularity, reusability, and maintainability. Here's how OOP principles can be applied:

• Encapsulation: Encapsulate data and functionality within objects to hide implementation details and expose only necessary interfaces.
• Inheritance: Utilize inheritance to create hierarchies of classes, promoting code reuse and facilitating polymorphism.
• Polymorphism: Implement polymorphism to enable objects of different classes to be treated uniformly through interfaces and inheritance.
• Abstraction: Abstract complex functionalities into class interfaces, allowing clients to interact with objects without needing to know their internal implementations.

33) Describe CDN and its uses?

Content Delivery Network (CDN) is a distributed network of servers strategically located across different geographical regions. Its uses include:

• Content Distribution: CDN caches content, such as web pages, images, videos, and other static files, closer to end-users, reducing latency and improving load times.
• Load Balancing: CDN distributes incoming traffic across multiple servers, balancing the load and preventing server overload.
• Security: CDNs often provide security features, such as DDoS protection and Web Application Firewall (WAF), safeguarding websites and applications against cyber threats.
• Global Scalability: CDN allows websites and applications to scale globally without the need for significant infrastructure investment, ensuring consistent performance across different regions.

34) Explain the term SLO?

Service Level Objective (SLO) is a key performance indicator that defines the reliability and availability goals of a service. It represents a target level of performance that a system aims to achieve within a specific time frame. SLOs are typically defined based on metrics such as uptime, response time, and error rate.

35) Define Service Level Indicators

A Service Level Indicator (SLI) is a way to gauge how well a service provider is serving a client. SLOs, in turn, serve as the foundation for SLAs, which serve as the foundation for SLAs (SLAs). An SLA metric is another name for an SLI.

Although the services offered by each system vary, common SLIs are used quite frequently. Other SLIs include:

• Durability (in storage systems).
• End-to-end latency (for complicated data processing systems, notable pipelines).
• Correctness.
• Common SLIs include latency, throughput, availability, and error rate.

36) What do you mean by TCP?

TCP stands for Transmission Control Protocol. It is a connection-oriented protocol used in computer networks for reliable and ordered delivery of data between devices. TCP provides features such as error checking, flow control, and congestion control to ensure that data packets are transmitted and received accurately and efficiently.

37) What is TCP best used for?

TCP is best used for applications that require reliable, ordered, and error-checked delivery of data, such as web browsing, email communication, file transfer (FTP), remote access (SSH), and online gaming. TCP ensures that data sent from one device is received accurately and in the correct order by the receiving device.

38) Explain iNodes?

Inodes, short for index nodes, are data structures used in Unix-like file systems to represent files and directories. Each file or directory on the file system is associated with an inode, which stores metadata about the file or directory, such as its permissions, ownership, size, and location on disk. Inodes also contain pointers to the data blocks where the actual file contents are stored.

39) What is an SLA(Service-Level Agreement)?

A Service-Level Agreement (SLA) is a contract between a service provider and a customer that defines the expected level of service quality, including performance metrics, uptime guarantees, response times, and penalties for failing to meet the agreed-upon service levels. SLAs help ensure accountability and establish clear expectations between parties.

40) What is SNAT and DNAT in networking?

SNAT (Source Network Address Translation) and DNAT (Destination Network Address Translation) are techniques used in computer networking to modify the source and destination IP addresses of packets as they pass through a network device, such as a router or firewall. SNAT changes the source IP address of outgoing packets, while DNAT changes the destination IP address of incoming packets, allowing for routing and security enhancements.

41) What do you mean by virtualization?

Virtualization is the process of creating virtual instances of computer hardware, software, storage, or network resources. It allows multiple virtual machines (VMs) or containers to run on a single physical server, enabling greater resource utilization, flexibility, and scalability. Virtualization abstracts physical hardware, allowing for the efficient allocation and management of computing resources.

42) What is a container on server?

A container on a server is a lightweight, portable, and isolated environment that encapsulates an application and its dependencies, enabling it to run consistently across different computing environments. Containers share the host operating system's kernel and resources, making them more efficient than traditional virtual machines. Containers provide a standardized and efficient way to package, deploy, and manage applications in a variety of environments.

43) Explain when you would use a hardlink instead of softlink?

Because changing the source does not delete the hardlink relationship. A hard link is helpful when the source file is moving about. On the other hand, a weak link is broken if the source is changed to a soft link. This is because softlink uses the source filename in its data section, hardlink shares the same inode.

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44) How will you secure your Docker containers?

You must adhere to the following rules to secure your Docker container:

• Choose third-party containers carefully
• Enable Docker content trust
• Set resource limits for your containers
• Consider a third-party security tool
• Use Docker Bench Security
   

45) Discuss the Best SRE Tools you know for each Stage/Level of DevOps.

The following SRE tools are suitable for each DevOps stage:

• Create: Source-control tools like GitHub
• Plan:  Pivotal, Jira, Tracker, and other task management tools
• Package: Container orchestration services like Mesosphere or Kubernetes.
• Verify: CI/CD tools like   CircleCI or Jenkins
• Configure: Tools like Ansible and Terraform
   

46) What is observability, and how to enhance organizations' systems observability?

Observability is essentially a discussion of how to measure and use an organization.

To enhance an organization's observability, you need to:

• Discover how your strategy makes sense of the data by distilling, filtering, and transforming it into valuable insights about the performance of your systems. Gain a clear understanding of what matters to a team.
• Recognize the many data kinds that come from an environment and determine which of them are pertinent to and valuable for your observability goals.
• Observability provides potentially helpful hints regarding the DevOps maturity level of an organization.

SRE Coding Interview Questions

47). Write a Python program to check if a given number is prime.

This program uses a simple loop to check if a number is prime by testing divisibility. It runs efficiently by checking divisors up to the square root of the number.

def is_prime(num):
   if num <= 1:
       return False
   for i in range(2, int(num ** 0.5) + 1):
       if num % i == 0:
           return False
   return True
number = int(input("Enter a number: "))
print(f"{number} is prime") if is_prime(number) else print(f"{number} is not prime")

48). Write a function to reverse a linked list in Python.

This function reverses a linked list by adjusting the pointers iteratively. It runs in O(n) time, where n is the length of the linked list.

class Node:
   def __init__(self, data):
       self.data = data
       self.next = None
def reverse_linked_list(head):
   prev = None
   current = head
   while current:
       next_node = current.next
       current.next = prev
       prev = current
       current = next_node
   return prev

49). Write a Python program to implement a basic queue using lists.

This code implements a basic queue using Python lists, where elements are added to the end and removed from the front.

class Queue:
   def __init__(self):
       self.queue = []
   def enqueue(self, item):
       self.queue.append(item)
   def dequeue(self):
       if not self.is_empty():
           return self.queue.pop(0)
       return "Queue is empty"
   def is_empty(self):
       return len(self.queue) == 0
q = Queue()
q.enqueue(10)
q.enqueue(20)
print(q.dequeue())  # Outputs: 10

50). Write a function to find the maximum element in an array.

This function iterates through an array and returns the maximum element. It operates with a time complexity of O(n).

def find_max(arr):
   max_val = arr[0]
   for num in arr:
       if num > max_val:
           max_val = num
   return max_val
arr = [10, 20, 30, 40, 50]
print(f"The maximum element is: {find_max(arr)}")

51). Write a Python function to sort an array using bubble sort.

Bubble sort repeatedly swaps adjacent elements if they are in the wrong order. Though simple, its time complexity is O(n^2), making it inefficient for large datasets.

def bubble_sort(arr):
   n = len(arr)
   for i in range(n):
       for j in range(0, n-i-1):
           if arr[j] > arr[j+1]:
               arr[j], arr[j+1] = arr[j+1], arr[j]
arr = [64, 34, 25, 12, 22, 11, 90]
bubble_sort(arr)
print("Sorted array is:", arr)

52). Write a Python function to check for balanced parentheses in an expression.

This function checks for balanced parentheses using a stack. It returns True if all parentheses are balanced and False otherwise.

def is_balanced(expression):
   stack = []
   pairs = {')': '(', '}': '{', ']': '['}
   for char in expression:
       if char in "({[":
           stack.append(char)
       elif char in ")}]":
           if not stack or stack.pop() != pairs[char]:
               return False
   return not stack

53). Implement a basic stack in Python.

This code implements a stack, where elements are added and removed from the top. The stack follows a LIFO (Last In, First Out) structure.

class Stack:
   def __init__(self):
       self.stack = []
   def push(self, item):
       self.stack.append(item)
   def pop(self):
       if not self.is_empty():
           return self.stack.pop()
       return "Stack is empty"
   def is_empty(self):
       return len(self.stack) == 0
s = Stack()
s.push(1)
s.push(2)
print(s.pop())  # Outputs: 2

54). Write a Python function to merge two sorted arrays.

This function merges two sorted arrays in O(n+m) time, where n and m are the sizes of the input arrays.

def merge_arrays(arr1, arr2):
   result = []
   i = j = 0
   while i < len(arr1) and j < len(arr2):
       if arr1[i] < arr2[j]:
           result.append(arr1[i])
           i += 1
       else:
           result.append(arr2[j])
           j += 1
   result.extend(arr1[i:])
   result.extend(arr2[j:])
   return result
arr1 = [1, 3, 5]
arr2 = [2, 4, 6]
print(merge_arrays(arr1, arr2))

SRE MCQ Questions

1) What is the main goal of SRE?

• A) Increase system complexity
• B) Enhance system reliability
• C) Focus on manual processes
• D) Reduce automation
  Answer: B) Enhance system reliability

2) Which metric defines the acceptable level of system reliability?

• A) SLA
• B) SLO
• C) SLI
• D) KPI
  Answer: B) SLO

3) What is the role of error budgets in SRE?

• A) To prevent changes
• B) To allow more system errors
• C) To balance reliability with innovation
• D) To increase downtime
  Answer: C) To balance reliability with innovation

4) Which of the following is a key SRE tool for monitoring systems?

• A) Docker
• B) Kubernetes
• C) Prometheus
• D) Jenkins
  Answer: C) Prometheus

5) What is an important SRE practice to reduce toil?

• A) Increase human intervention
• B) Automate repetitive tasks
• C) Focus on manual scaling
• D) Disable monitoring tools
  Answer: B) Automate repetitive tasks

6) What is the primary responsibility of an SRE?

• A) Writing application code
• B) Ensuring system reliability
• C) Managing marketing campaigns
• D) Reducing system performance
  Answer: B) Ensuring system reliability

7) Which tool is commonly used for container orchestration in SRE?

• A) Ansible
• B) Terraform
• C) Kubernetes
• D) Nagios
  Answer: C) Kubernetes

8) What does SLI stand for in the context of SRE?

• A) System-Level Integration
• B) Service-Level Indicator
• C) Software-Level Indicator
• D) Service-Line Integration
  Answer: B) Service-Level Indicator

9) In SRE, what is a runbook used for?

• A) Developing new features
• B) Automating code deployment
• C) Documenting incident response procedures
• D) Monitoring system performance
  Answer: C) Documenting incident response procedures

10) What is a key benefit of automation in SRE?

• A) Increased system complexity
• B) Reduced human error
• C) Manual intervention
• D) Delayed system response
  Answer: B) Reduced human error

Conclusion

This article explores a variety of SRE interview questions tailored for both freshers and experienced candidates. The freshers section consists of fundamental concepts essential for newcomers to the field, while the experienced section delves deeper into advanced topics that evaluate your technical expertise. By preparing with these questions, you'll strengthen your interview skills and demonstrate a solid understanding of site reliability engineering principles.

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