Hiring guide for Lustre Engineers

Lustre Developer Hiring Guide

Lustre is a formally defined, declarative, and synchronous programming language that was developed in the early 1980s by Nicolas Halbwachs and his team at VERIMAG, a research center in Grenoble, France. It was designed for programming reactive systems—systems that continuously interact with their environment—such as automatic control and signal processing systems. Lustre's key features include its ability to express parallelism and preemption naturally without explicit synchronization mechanisms. The language has been used as the basis for SCADE (Safety Critical Application Development Environment), an industry-standard tool used widely in critical applications like avionics software development. Its design principles have also influenced other languages such as Esterel and Signal.

Ask the right questions secure the right Lustre talent among an increasingly shrinking pool of talent.

First 20 minutes

General Lustre app knowledge and experience

The first 20 minutes of the interview should seek to understand the candidate's general background in Lustre application development, including their experience with various programming languages, databases, and their approach to designing scalable and maintainable systems.

Can you explain the architecture of Lustre file system?
Lustre file system is composed of three major components: Metadata Server (MDS), Object Storage Servers (OSS) and clients. MDS manages the namespace, handles the creation, deletion, and attributes of files and directories. OSS manage the file data handling, storing and retrieving. Clients are the compute nodes that use the file system.
What is the role of Metadata Server (MDS) in Lustre?
The Metadata Server (MDS) in Lustre manages the metadata, which includes file names, directories, permissions, and file layout. It handles operations such as file and directory creation, deletion, and permission changes.
How would you handle data recovery in Lustre?
Lustre provides data recovery through RAID, replication, and backup. RAID is used to protect against disk failures. Replication can be used to create copies of data on different servers. Backup can be performed using traditional backup software.
What is striping in Lustre and how does it work?
Striping in Lustre is a method of distributing the data of a single file across multiple Object Storage Targets (OSTs). This allows for increased performance by enabling concurrent read and write operations.
Describe the difference between Lustre and other distributed file systems.
Lustre differs from other distributed file systems in its scalability and performance. It is designed for large-scale cluster computing, with the ability to scale to thousands of nodes and petabytes of storage. It also provides high performance through parallel I/O and striping.
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What you’re looking for early on

Does the candidate have a strong understanding of Lustre file systems?
Has the candidate demonstrated problem-solving skills during the interview?
Is the candidate able to communicate effectively?
Does the candidate have experience with Linux and other relevant technologies?

Next 20 minutes

Specific Lustre development questions

The next 20 minutes of the interview should focus on the candidate's expertise with specific backend frameworks, their understanding of RESTful APIs, and their experience in handling data storage and retrieval efficiently.

What are the key benefits of using Lustre?
Key benefits of Lustre include high performance, scalability, and flexibility. Lustre provides high throughput for large data sets and can scale to thousands of nodes and petabytes of storage. It also supports a variety of network and storage hardware.
How would you improve the performance of a Lustre file system?
Performance of a Lustre file system can be improved by optimizing the network, increasing the number of OSTs, enabling striping, and tuning various parameters such as the I/O size and the number of RPCs in flight.
What is the role of LNET in Lustre?
LNET (Lustre Networking) is the networking layer of Lustre. It provides a unified interface for communication between nodes, regardless of the underlying network technology. It also handles routing and failover.
How would you troubleshoot a slow Lustre file system?
Troubleshooting a slow Lustre file system involves checking the network for congestion, examining the server load, checking the disk usage and health, and reviewing the configuration for any potential issues.
What is the significance of Object Storage Targets (OSTs) in Lustre?
Object Storage Targets (OSTs) in Lustre are the storage devices where the actual file data is stored. They are managed by Object Storage Servers (OSS). Multiple OSTs can be associated with a single file to enable striping and improve performance.
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The ideal back-end app developer

What you’re looking to see on the Lustre engineer at this point.

At this point, a skilled Lustre engineer should demonstrate strong problem-solving abilities, proficiency in Lustre programming language, and knowledge of software development methodologies. Red flags include lack of hands-on experience, inability to articulate complex concepts, or unfamiliarity with standard coding practices.

Digging deeper

Code questions

These will help you see the candidate's real-world development capabilities with Lustre.

What does this simple Lustre code do?
node main (x, y: int) returns (z: int);
z = x + y;
This code defines a Lustre node named 'main' that takes two integer inputs 'x' and 'y', and returns an integer 'z'. The value of 'z' is the sum of 'x' and 'y'.
What will be the output of this Lustre code if input values are 5 and 6?
node main (x, y: int) returns (z: bool);
z = x > y;
The output will be 'false'. This code defines a Lustre node that takes two integer inputs and returns a boolean. The boolean 'z' is the result of the comparison 'x > y'. Since 5 is not greater than 6, the output will be 'false'.
What does this Lustre code do with the array of integers?
node main (x: int^3) returns (y: int);
y = x[1] + x[2] + x[3];
This code defines a Lustre node that takes an array of three integers and returns an integer. The output 'y' is the sum of all the elements in the input array 'x'.
What does this Lustre code do in terms of concurrency?
node main (x, y: int) returns (z: int);
z = if x > y then x else y;
This code defines a Lustre node that takes two integer inputs and returns an integer. The output 'z' is the larger of the two inputs. Lustre is a synchronous language, so this operation is atomic and concurrency-safe, i.e., it will always return a consistent result regardless of the timing of input changes.

Wrap-up questions

Final candidate for Lustre Developer role questions

The final few questions should evaluate the candidate's teamwork, communication, and problem-solving skills. Additionally, assess their knowledge of microservices architecture, serverless computing, and how they handle Lustre application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

How would you secure a Lustre file system?
Securing a Lustre file system involves implementing network security measures, managing user permissions appropriately, keeping the system and software up-to-date, and regularly monitoring and auditing the system for any suspicious activity.
Describe the difference between synchronous and asynchronous I/O in Lustre.
Synchronous I/O in Lustre means that the I/O operations are performed immediately and the function does not return until the operation is complete. Asynchronous I/O, on the other hand, allows the function to return immediately after the operation is initiated, without waiting for it to complete.
What are the key considerations when designing a Lustre file system?
Key considerations when designing a Lustre file system include the expected data volume, the number of clients, the network infrastructure, the required performance, and the hardware capabilities.

Lustre application related

Product Perfect's Lustre development capabilities

Beyond hiring for your Lustre engineering team, you may be in the market for additional help. Product Perfect provides seasoned expertise in Lustre projects, and can engage in multiple capacities.