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Doble Engineering Software Engineer Interview Guide

Doble Engineering Software Engineer interview guide: reported rounds, questions and how candidates describe the process.

The 60-second brief

A Software Engineer at Doble Engineering plays a critical role in ensuring the safety, reliability, and efficiency of the global electric power grid. Unlike typical consumer-facing software roles, engineering at Doble Engineering involves building highly specialized diagnostic systems, monitoring applications, and analytical tools used by utility companies worldwide. The software you develop directly interfaces with physical hardware, processes complex sensor data, and helps power engineers prevent catastrophic grid failures. The impact of this position is felt across a wide range of products, from legacy desktop diagnostics to modern, cloud-based web applications.

This guide is scoped to a Software Engineer candidate at Doble Engineering.

Focus areas

  • Desktop-to-web migration (legacy modernization)
  • Domain: Protection engineering (power protection)
  • Scalability

The Doble Engineering interview process

Doble Engineering candidates report 6 rounds over 4-6 weeks. The stages below are what candidates describe, not a published process.

Recruiter Call

Initial conversation with a recruiter to discuss the candidate's background and the role.

What to demonstrate

  • Initial conversation with a recruiter to discuss the candidate's background and the role
  • Depth in Desktop-to-web migration (legacy modernization)

How to prepare

  • Be able to walk your CV end to end in two minutes, and say why this company specifically.
  • Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.

Technical Screening

Technical screening round with a hiring manager to assess engineering capabilities.

What to demonstrate

  • Technical screening round with a hiring manager to assess engineering capabilities
  • Depth in Desktop-to-web migration (legacy modernization)

How to prepare

  • Answer aloud and timed: How would you approach identifying and resolving a memory leak in a long-running server-side application?
  • Answer aloud and timed: Describe your experience working with multi-threaded programming and how you handle race conditions.

Take-home Coding Assignment

Candidates complete a coding assignment to demonstrate their hands-on coding style.

What to demonstrate

  • Candidates complete a coding assignment to demonstrate their hands-on coding style
  • Depth in Desktop-to-web migration (legacy modernization)

How to prepare

  • Answer aloud and timed: How do you ensure your code remains optimized when processing large, continuous streams of real-time diagnostic data?
  • Answer aloud and timed: How would you approach migrating a legacy, server-centric desktop application to a modern, scalable web-based architecture?

Technical Panel Interviews

Deeper technical interviews that may include whiteboard exercises and project discussions.

What to demonstrate

  • Deeper technical interviews that may include whiteboard exercises and project discussions
  • Depth in Desktop-to-web migration (legacy modernization)

How to prepare

  • Answer aloud and timed: What architectural patterns would you use to decouple a monolithic backend into modular, maintainable services?
  • Answer aloud and timed: Describe a time you had to troubleshoot and optimize a poorly performing database query or data pipeline.

Cross-functional Conversations

Discussions with cross-functional team members, potentially including an onsite tour.

What to demonstrate

  • Discussions with cross-functional team members, potentially including an onsite tour
  • Depth in Desktop-to-web migration (legacy modernization)

How to prepare

  • Answer aloud and timed: How do you design user interfaces that can cleanly display highly dense, complex engineering and diagnostic metrics to field technicians?
  • Answer aloud and timed: What strategies do you use to ensure backward compatibility when rewriting a core product legacy system?

Onsite Tour

NDA-protected tour of the testing laboratories to see the hardware supported by the software.

What to demonstrate

  • NDA-protected tour of the testing laboratories to see the hardware supported by the software
  • Depth in Desktop-to-web migration (legacy modernization)

How to prepare

  • Answer aloud and timed: What first motivated you to become a software developer, and how has your career journey shaped your engineering philosophy?
  • Answer aloud and timed: Where do you see yourself in the next five years, and how does this role fit into your professional growth?

Where candidates lose points

Emphasize Low-Dependency Solutions

When discussing coding practices, highlight your ability to solve problems using core language features. Avoid jumping immediately to third-party libraries or frameworks unless specifically asked, as the team values lightweight, highly optimized code.

Prepare Your Personal Narrative

Be ready to talk about why you became a developer. The hiring managers are genuinely interested in your personal motivation, your passion for engineering, and how you approach professional growth.

Ask About the Hardware Integration

Show curiosity about how the software you will build interfaces with Doble Engineering's physical diagnostic hardware. This demonstrates that you understand the unique nature of their industrial software environment.

Budget more time than the estimated two hours for the take-home assessment

Candidates who deliver highly polished, production-ready code stand out significantly.

Questions & practice

How do you implement a custom data structure or algorithm in Java or C++ without relying on third-party librar

Medium · Core Software Engineering & Language Fun

How do you implement a custom data structure or algorithm in Java or C++ without relying on third-party libraries?

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Explain the key differences between memory management in C++ and garbage collection in Java.

Medium · Core Software Engineering & Language Fun

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

Describe your experience working with multi-threaded programming and how you handle race conditions.

Medium · Core Software Engineering & Language Fun

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

How do you ensure your code remains optimized when processing large, continuous streams of real-time diagnosti

Medium · Core Software Engineering & Language Fun

How do you ensure your code remains optimized when processing large, continuous streams of real-time diagnostic data?

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

Write the update path that detects a concurrent edit

Medium · optimistic concurrency · transactional outbox · audit history

resource carries version INT NOT NULL DEFAULT 1. resource_revision holds revision_id, resource_id, version, actor_user_id, change_kind, patch JSONB, request_id, created_at with UNIQUE (resource_id, version). outbox_event holds aggregate_type, aggregate_id, aggregate_version, event_type, payload, status. A PUT carries the version the client read. Write the exact statements for the single transaction that applies the edit, records the revision and enqueues 'resource.updated', and give the handler's branch on zero affected rows. Then say what PostgreSQL 16 does under READ COMMITTED when two of these updates hit one row at once.

Approach

  1. One transaction, three writes, no network call inside it: UPDATE resource SET title = $3, version = version + 1, updated_at = now() WHERE resource_id = $1 AND tenant_id = $4 AND version = $2; then INSERT the resource_revision row at version $2 + 1; then INSERT the outbox_event row at the same aggregate_version. The event goes to a table rather than a broker because no transaction spans both.
  2. Branch on the affected-row count before doing anything else. Zero has three causes — stale version, wrong tenant, row gone — so re-read once and map to 409 carrying the current version, or 404 for an id outside the caller's tenant, which also stops the endpoint confirming that another tenant's id exists.
  3. State the engine behaviour instead of assuming it. Under READ COMMITTED the second UPDATE blocks on the row lock, and when the first commits PostgreSQL re-evaluates the WHERE clause against the newly committed row, so the version predicate now fails and the statement reports zero rows. Under REPEATABLE READ the identical collision raises SQLSTATE 40001 instead, so the handler must fold both shapes into one conflict response.
  4. Keep UNIQUE (resource_id, version) even though the predicate already serialises writers. It is what makes a lost update unwritable if any other path ever reaches the revision table, and it converts a logic bug into 23505 rather than into a silently missing history row.

Follow-up

  • A client sends the version it read ten minutes ago and the resource has moved three versions. What is in your 409 so it can resolve the conflict without a full re-fetch?
  • Two editors, two disjoint fields, no overlap. Does your answer still refuse the second write, and should it?

Keep soft-deleted accounts from blocking re-registration

Easy · soft delete · unique constraints · engine differences

app_user holds user_id, tenant_id, email CITEXT, password_hash (NULL for SSO principals), email_verified_at, auth_version, status ('invited','active','suspended','deactivated'), created_at, updated_at, deleted_at. Two live accounts for one address inside a tenant must be impossible, but an address freed by a soft delete must be reusable, and the same tenant may delete and re-register it repeatedly. Write the uniqueness DDL for PostgreSQL 16, then the equivalent for MySQL 8 where partial indexes do not exist, and say what each permits once three deleted rows already hold that address.

Approach

  1. Start from what is actually unique: not (tenant_id, email), but (tenant_id, email) among live rows. PostgreSQL says that directly — CREATE UNIQUE INDEX app_user_live_email ON app_user (tenant_id, email) WHERE deleted_at IS NULL. A full constraint over the same two columns burns the address permanently the first time someone deletes an account.
  2. Keep case-insensitivity in the type or the index, never in the application: CITEXT as given, or UNIQUE (tenant_id, lower(email)) as an expression index where the extension is unavailable. A case-sensitive unique column is exactly how two accounts for one human appear.
  3. For MySQL 8 the predicate has to move inside the key: add a discriminator column that is a constant 0 while the row is live and is set to user_id on delete, with UNIQUE (tenant_id, email, deleted_marker). Live rows share the constant and still collide; deleted rows differ from each other and stop colliding.
  4. State the NULL variant and its dependency: leaving the marker NULL for deleted rows also works, because a unique index treats NULLs as distinct — true in MySQL, and true in PostgreSQL only under the default NULLS DISTINCT, which PostgreSQL 15 lets you reverse. Check the polarity against the three existing deleted rows: constant-on-live is what preserves the collision you want, and reversing it silently admits duplicate live accounts.

Follow-up

  • A deleted account re-registers with the same address the next day. Do the old resource rows follow the new user_id, and how does the API keep the two principals apart?
  • How do you honour an erasure request while resource_revision.actor_user_id still references this table?

How would you approach migrating a legacy, server-centric desktop application to a modern, scalable web-based

Medium · Web App Migration & Architecture

How would you approach migrating a legacy, server-centric desktop application to a modern, scalable web-based architecture?

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

What architectural patterns would you use to decouple a monolithic backend into modular, maintainable services

Medium · Web App Migration & Architecture

What architectural patterns would you use to decouple a monolithic backend into modular, maintainable services?

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

How do you design user interfaces that can cleanly display highly dense, complex engineering and diagnostic me

Medium · Web App Migration & Architecture

How do you design user interfaces that can cleanly display highly dense, complex engineering and diagnostic metrics to field technicians?

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

What strategies do you use to ensure backward compatibility when rewriting a core product legacy system?

Medium · Web App Migration & Architecture

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

What is your understanding of Protection & Control (P&C) systems or power grid diagnostics?

Medium · Domain & Industry Alignment

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

How do you approach designing software that must interface directly with physical testing hardware or sensor d

Medium · Domain & Industry Alignment

How do you approach designing software that must interface directly with physical testing hardware or sensor devices?

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

How would you approach identifying and resolving a memory leak in a long-running server-side application?

Medium · Core Software Engineering & Language Fun

Approach

  1. Establish what changed and when, before forming any theory.
  2. Pick a bisection that eliminates candidates whichever way it turns out.
  3. Check the instrumentation before believing the symptom.
  4. Separate the trigger from the cause; the deploy is rarely the bug.

Follow-up

  • What would you look at first, and what would it rule out?
  • How would you tell a cause from a coincidence here?

Suggested practice checklist

Built from the rounds and topics Doble Engineering candidates report.

Day 1 — Map the Doble Engineering loop

  • Write out the reported sequence: Recruiter Call, Technical Screening, Take-home Coding Assignment, Technical Panel Interviews, Cross-functional Conversations, Onsite Tour.
  • For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.

Deliverable: A one-page map of the 6 reported rounds, with the weakest marked.

Day 2 — Work Desktop-to-web migration (legacy modernization)

  • Spend the session on Desktop-to-web migration (legacy modernization), which Doble Engineering candidates report being tested on.
  • Write one worked example in Desktop-to-web migration (legacy modernization) and time yourself on it.

Deliverable: One timed worked example in Desktop-to-web migration (legacy modernization).

Day 3 — Work Domain: Protection engineering (power protection)

  • Spend the session on Domain: Protection engineering (power protection), which Doble Engineering candidates report being tested on.
  • Write one worked example in Domain: Protection engineering (power protection) and time yourself on it.

Deliverable: One timed worked example in Domain: Protection engineering (power protection).

Day 4 — Work Scalability

  • Spend the session on Scalability, which Doble Engineering candidates report being tested on.
  • Write one worked example in Scalability and time yourself on it.

Deliverable: One timed worked example in Scalability.

Day 5 — Answer out loud: Core Software Engineering & Language Fundamentals

  • Answer aloud, timed: How do you implement a custom data structure or algorithm in Java or C++ without relying on third-party libraries?
  • Answer aloud, timed: Explain the key differences between memory management in C++ and garbage collection in Java.

Deliverable: Spoken answers to 2 reported Core Software Engineering & Language Fundamentals question(s), under time.

Day 6 — Answer out loud: Web App Migration & Architecture

  • Answer aloud, timed: How would you approach migrating a legacy, server-centric desktop application to a modern, scalable web-based architecture?
  • Answer aloud, timed: What architectural patterns would you use to decouple a monolithic backend into modular, maintainable services?

Deliverable: Spoken answers to 2 reported Web App Migration & Architecture question(s), under time.

Day 7 — Answer out loud: Behavioral & Personal Journey

  • Answer aloud, timed: What first motivated you to become a software developer, and how has your career journey shaped your engineering philosophy?
  • Answer aloud, timed: Where do you see yourself in the next five years, and how does this role fit into your professional growth?

Deliverable: Spoken answers to 2 reported Behavioral & Personal Journey question(s), under time.

Behavioural preparation

Behavioural rounds judge the decision you made and what it cost.

Describe a time you had to troubleshoot and optimize a poorly performing database query or data pipeline.

Medium · Web App Migration & Architecture

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

What first motivated you to become a software developer, and how has your career journey shaped your engineeri

Medium · Behavioral & Personal Journey

What first motivated you to become a software developer, and how has your career journey shaped your engineering philosophy?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Where do you see yourself in the next five years, and how does this role fit into your professional growth?

Medium · Behavioral & Personal Journey

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Describe a situation where you had to work closely with cross-functional teams, such as hardware engineers or

Medium · Behavioral & Personal Journey

Describe a situation where you had to work closely with cross-functional teams, such as hardware engineers or client services, to solve a complex issue.

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

How do you handle situations where there is no clear direction or documentation for a system you are tasked to

Medium · Behavioral & Personal Journey

How do you handle situations where there is no clear direction or documentation for a system you are tasked to modify?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Why are you interested in working on industrial power grid diagnostics rather than standard consumer SaaS prod

Medium · Behavioral & Personal Journey

Why are you interested in working on industrial power grid diagnostics rather than standard consumer SaaS products?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Describe your experience working with industrial communication protocols or handling raw binary data formats.

Medium · Domain & Industry Alignment

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?