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Nutshell Backend Interview Questions (2021)

To start, we ask all candidates to answer the following questions. A paragraph or two each is probably about right:

  1. What's your proudest achievement? It can be from work, a side project, or something unrelated to tech. We're interested in knowing about what you think is noteworthy and motivating.
  2. Tell us about an interesting work-related book, article, or presentation that you saw recently. Tell us why, give us a recommendation, and sell us on it!
  3. From what you’ve seen on our web site, write about who Nutshell’s customers are, and what problems they’re looking to solve.
  4. Describe something that you do outside of work that's least similar to what you do at work.
  5. Describe something you do at work that's furthest from your official description.
  6. Tell us about the last time you had to reconsider a closely-held opinion. What caused your change in thinking?

To finish, below is a list of 8 questions that we ask all backend candidates to answer. These aren’t meant to be trick questions, and some are purposefully a bit opened ended to help orient a discussion during subsequent interviews.

To help set expectations, we believe this should take under 2-3 hours to complete. We understand that you have other responsibilities, so if you think you’ll need more than 3-4 days, just let us know when you expect to send a reply.

You might find gist.github.com a convenient way to send us your work.

Questions

  • We use “Feature Flags” to release code which will only run for certain users. Can you explain how this process might work and how it could be implemented?

  • Can you briefly explain a multi-tenant data storage architecture, and some pros/cons?

  • What is “PSR”? What is “PSR-7”?

  • Can you explain strict types in PHP, including how to enable and use them?

  • Can you describe what this code is doing? Can you identify any issues it may encounter in production?

    public function canAccess(string $cacheId): bool {
        $memcache = $this->getCache();

        $attempts = json_decode($memcache->get($cacheId), true) ?: [];
        if (count($attempts) >= $this->limit) {
            return false;
        }

        return true;
    }

    public function recordRequest(string $cacheId): void {
        $memcache = $this->getCache();

        $attempts = json_decode($memcache->get($cacheId), true) ?: [];
        $attempts[] = time();
        $memcache->set($cacheId, json_encode($attempts), $this->ttl);
    }

  • git status reports “Your branch and 'origin/feature' have diverged.” What happened and how do you handle this situation?

  • Our Database Object–relational mapping (ORM) uses a shared cache to store table/column metadata for performance. When a new release introduces a change, the cache will need to be cleared and re-written to contain the new data. During a deployment, old code and new code will be running simultaneously. If the cache is cleared on deploy, the running old code will write old cache data. How do you handle this?

  • We use GitHub for code review so we can leave inline comments and provide written feedback for teammates. Pretending the following code was submitted as a pull request, what kind of feedback would you leave? What do you think could be improved, and how would you devlier that feedback?

/**
 * This made up function takes an array of id/type pairs and attempts to look up corresponding
 * models from the database and return them as an array. Should throw an exception if one of the
 * filter params does not find a corresponding model
 *
 * We can assume the format of the filter params are correct (integer for id, string for type)
 *
 * An example input:
 * [
 *	['id' => 13, 'type' => 'tags'],
 * 	['id' => 11, 'type' => 'tags'],
 * 	['id' => 2, 'type' => 'sources'],
 * ]
 *
 * @param  string $parameters - Array of filter params
 * @return array              - List of models
 */
function getModelsFromFilterParams(array $filterParams) {
	$error = false;
	$models = [];
	foreach ($params as $param) {
		// This function looks up a model by id and type – will return
		// the model if found, otherwise null.
		$model = Example::getModelByIdAndType($param['id'], $param['type']);
		if (!$model) {
			$error = $param;
		}

		$models = array_push($models, $model);
	}

	if ($error) {
		throw new Exception("Invalid filter – could not find model with id {$param['id']} of type {$param['type']}");
	}

	return $models;
}