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Ask the right questions to secure the right Erlang OTP talent among an increasingly shrinking pool of talent.
Erlang OTP (Open Telecom Platform) is a programming language developed by Ericsson in the late 1980s to address the needs of telecommunication systems. It is a concurrent, functional language designed for building scalable, fault-tolerant applications. The language's key features include hot swapping, where code can be changed without stopping the system, and its ability to handle large numbers of lightweight processes. Erlang OTP has been used in various sectors beyond telecoms, such as banking, e-commerce and computer telephony. Its robustness and efficiency have made it a popular choice for high-availability systems (source: "Erlang Programming" by Francesco Cesarini and Simon Thompson).
The next 20 minutes of the interview should attempt to focus more specifically on the development questions used, and the level of depth and skill the engineer possesses.
State in a gen_server is handled using its callback functions. The state is passed as an argument to the callback functions and can be updated and returned from these functions to maintain state across different function calls.
gen_server is a behavior module for implementing the server of a client-server relation. gen_event is a behavior module for implementing event handling functionality. The main difference is that gen_server is used for handling requests and sending responses, while gen_event is used for handling events.
Some of the design principles of OTP include behaviors, which are formalized design patterns; supervision trees, which provide fault-tolerance; and applications, which are a packaging mechanism that allows developers to bundle related components together.
Supervision trees are a fault-tolerance mechanism in Erlang OTP. They are a hierarchical arrangement of processes where parent processes, known as supervisors, monitor the behavior of their child processes and take appropriate action if they fail.
The main components of OTP are the Erlang runtime system, a number of ready-to-use components mainly written in Erlang, and a set of design principles for Erlang programs.
Erlang is a functional programming language. A good understanding of functional programming concepts is necessary to write effective Erlang code.
Writing clean, efficient code is important for maintainability, readability, and performance. This shows the candidate's attention to detail and commitment to high quality work.
Erlang is often used in distributed systems, where tasks are divided among multiple computers. Understanding distributed systems indicates the candidate's ability to work on large-scale, complex projects.
Debugging is a critical skill for any developer. The ability to identify and fix issues in Erlang code is necessary for maintaining code quality and efficiency.
Erlang is known for its designs around concurrent programming. Experience in this area shows that the candidate can effectively handle tasks that require multiple computations to happen simultaneously.
This is crucial as Erlang OTP (Open Telecom Platform) is a set of Erlang libraries, which consists of the Erlang runtime system, a number of ready-to-use components mainly written in Erlang, and a set of design principles for Erlang programs. A deep understanding of this shows the candidate's expertise and ability to handle complex tasks.
The next 20 minutes of the interview should attempt to focus more specifically on the development questions used, and the level of depth and skill the engineer possesses.
Synchronous communication in Erlang OTP is when a process sends a message to another process and waits for a reply before continuing. Asynchronous communication is when a process sends a message to another process and continues without waiting for a reply.
The handle_call function is used to handle synchronous requests to the gen_server. It takes three arguments: the request, the client's process ID, and the server's current state. It returns a tuple that includes the reply to the client and the updated state.
Errors in a supervision tree are handled by the supervisor process. When a child process fails, the supervisor can choose to restart the child process, restart all child processes, or terminate all child processes and itself.
There are two types of process links in Erlang OTP: one-to-one links and one-to-many links. One-to-one links are created with the link function, while one-to-many links are created with the group_leader function.
The init function is called when the gen_server is started. It initializes the server's state and can also set options for the server.
A skilled Erlang OTP engineer should demonstrate strong knowledge of Erlang language, proficiency in OTP frameworks and understanding of concurrent programming. They should be able to design, build and maintain scalable systems. Red flags would include lack of practical experience or inability to solve complex problems.
add(X, Y) -> X + Y.{ok, {Year, Month, Day}} = erlang:localtime().[X || X <- [1,2,3,4,5,6,7,8,9,10], X rem 2 == 0].spawn(fun() -> io:format('Hello from another process~n') end).-record(person, {name, age}).-module(test).
-export([start/0]).
start() ->
Pid = spawn(fun loop/0),
Pid ! {self(), hello},
receive
{Pid, Msg} ->
io:format('Received ~p~n', [Msg])
end.
loop() ->
receive
{From, Msg} ->
From ! {self(), Msg},
loop()
end.The final few interview questions for a Erlang OTP candidate should typically focus on a combination of technical skills, personal goals, growth potential, team dynamics, and company culture.
Designing a distributed system using Erlang OTP involves using its built-in support for distributed programming. This includes using distributed Erlang nodes, global process names, and distributed applications. The design should also take into account fault-tolerance, scalability, and consistency requirements.
Some ways to improve the performance of an Erlang OTP application include optimizing the code, using native compiled code, adjusting the scheduler settings, and using more efficient data structures.
If a process in a supervision tree is frequently crashing, it may be necessary to adjust the supervisor's restart strategy or the maximum restart intensity. If the problem persists, it may be necessary to investigate the cause of the crashes and fix the underlying issue.
The handle_info function is used to handle all messages sent to the gen_server that are not requests or responses. It takes two arguments: the message and the server's current state. It returns a tuple that includes the updated state.
A finite state machine can be implemented in Erlang OTP using the gen_statem behavior. This involves defining the states and transitions of the machine in the callback functions of a gen_statem module.
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