cswork / libraryOpen practice workspace

Interview guides · Sunayu

Sunayu Software Engineer Interview Guide

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

The 60-second brief

At Sunayu, a Software Engineer does not just write code; they build and secure the technological backbone of national security and defense operations. Working directly with the United States Intelligence Community (IC) and the Department of Defense (DoD), engineers at Sunayu design, deploy, and maintain highly complex, mission-critical systems. These systems process massive, real-time data streams, optimize signals intelligence (SIGINT), manage high-performance graphics processing unit (GPU) pipelines, and architect secure cloud and network environments. The impact of this role is immediate and profound. A single optimization in a signal-processing pipeline or a security enhancement in a cloud architecture can directly affect tactical decision-making and national security outcomes.

This guide is scoped to a Software Engineer candidate at Sunayu.

Focus areas

  • Secure Software Engineering
  • TS/SCI (Security Clearance Requirements)
  • Network Engineering

The Sunayu interview process

Sunayu candidates report 4 rounds over 3-5 weeks. The stages below are what candidates describe, not a published process.

Security Clearance Verification

Thorough verification of your security clearance status as many positions require active TS/SCI with Polygraph clearances.

What to demonstrate

  • Thorough verification of your security clearance status as many positions require active TS/SCI with Polygraph clearances
  • Depth in Secure Software Engineering

How to prepare

  • Answer aloud and timed: Describe how you would handle thread safety and synchronization in a high-throughput, multi-threaded Java application.
  • Answer aloud and timed: What are the primary differences between optimistic and pessimistic locking, and when would you use each in a distributed system?

Initial Screening

An initial assessment to evaluate your qualifications and fit for the role.

What to demonstrate

  • An initial assessment to evaluate your qualifications and fit for the role
  • Depth in Secure Software Engineering

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 Assessments

Tailored technical evaluations based on your specific engineering track.

What to demonstrate

  • Tailored technical evaluations based on your specific engineering track
  • Depth in Secure Software Engineering

How to prepare

  • Answer aloud and timed: How do you design an API that remains backward-compatible while undergoing significant underlying database schema changes?
  • Answer aloud and timed: Explain the pipeline architecture required to ingest, process, and store high-frequency signal data with minimal packet loss.

Comprehensive Panel Interview

A detailed interview with a panel to assess your overall suitability for the position.

What to demonstrate

  • A detailed interview with a panel to assess your overall suitability for the position
  • Depth in Secure Software Engineering

How to prepare

  • Answer aloud and timed: How would you leverage GPU computing (using CUDA or OpenCL) to accelerate parallelizable data processing tasks compared to traditional CPU processing?
  • Answer aloud and timed: Describe the architectural tradeoffs between using a relational database versus a NoSQL key-value store for storing metadata generated by real-time sensor streams.

Where candidates lose points

Highlight Cleared Experience

If you have previously worked in a SCIF, managed air-gapped deployments, or navigated the Risk Management Framework (RMF), make sure to highlight this. Understanding the operational constraints of cleared spaces is a major differentiator.

Use the STAR Method

When answering behavioral questions, structure your responses using the Situation, Task, Action, and Result framework. Focus heavily on the Action you personally took and the quantifiable Result of your work.

When discussing past projects, ensure you do not disclose any classified or proprietary information

Focus on the high-level engineering methodologies, architectural patterns, and technologies used rather than specific mission details.

Questions & practice

Describe how you would handle thread safety and synchronization in a high-throughput, multi-threaded Java appl

Medium · Core Software Engineering & Java

Describe how you would handle thread safety and synchronization in a high-throughput, multi-threaded Java application.

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?

Explain how Java's garbage collection works, and how you would tune JVM parameters to minimize latency in a re

Medium · Core Software Engineering & Java

Explain how Java's garbage collection works, and how you would tune JVM parameters to minimize latency in a real-time data processing system.

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 manage memory allocation and data transfer overhead between the host CPU and the GPU device in high

Medium · Systems & Signals Processing

How do you manage memory allocation and data transfer overhead between the host CPU and the GPU device in high-performance applications?

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?

Denormalise tenant onto revisions and backfill it live

Hard · denormalisation · online migration · backfill

resource_revision (revision_id, resource_id, version, actor_user_id, change_kind, patch, request_id, created_at) has 400M rows and no tenant column; tenant_id lives only on resource. Two reads need it: a tenant-scoped audit feed ordered by created_at DESC, and an offboarding purge. Both join back to resource today. Justify adding tenant_id to resource_revision against those two reads, name the anomaly the copy introduces and the constraint that prevents it, then give the ordered migration for a live table taking 1.2k writes/second — the lock each step takes, how the backfill is batched, and where each step stops being reversible. PostgreSQL 16.

Approach

  1. Justify from the access path rather than from taste. Without the column, the audit feed either scans resource_revision by created_at and discards other tenants' rows, or resolves the tenant's resource_ids first and probes with them — both proportional to the tenant's whole history rather than to one page. With (tenant_id, created_at DESC, revision_id DESC) it is a seek that stops at 50 rows, and the purge becomes a ranged delete instead of a join.
  2. Name the cost exactly: a second copy of a fact can disagree with the first. Make the disagreement unwritable rather than documented — add UNIQUE (resource_id, tenant_id) on resource so it can serve as a foreign-key target, then FOREIGN KEY (resource_id, tenant_id) REFERENCES resource (resource_id, tenant_id) on the revision table. A revision can then only ever carry its parent's tenant.
  3. Step one, expand: ALTER TABLE resource_revision ADD COLUMN tenant_id BIGINT NULL, with no default, so it is a catalogue change and no rewrite. It still needs ACCESS EXCLUSIVE for an instant, and that instant queues behind the longest open transaction on the table while every later query queues behind it — set lock_timeout to 2s and retry rather than wait.
  4. Step two, dual-write: deploy the writer that populates tenant_id on every new revision while reads still use the join. Reversible by redeploying the previous build, because nothing reads the column yet.

Follow-up

  • The backfill is half finished and a rollback is required. What state is the table in, and what does the previous build do with a half-populated column?
  • How do you verify the backfill actually finished, given rows are still being inserted while it runs?

Hold a per-tenant active cap against concurrent creates

Hard · write skew · isolation levels · constraints

A tenant on the standard plan may hold at most 50 resources with status='active'. The create handler runs SELECT count(*) FROM resource WHERE tenant_id = $1 AND status = 'active', compares to 50, then inserts. Two creates arrive 3 ms apart on different instances and the tenant lands at 51. Name the anomaly, say whether PostgreSQL 16 READ COMMITTED or REPEATABLE READ prevents it and why, then give an implementation that holds the cap at READ COMMITTED with the exact statements. Finally, say what changes when the cap is 'at most one running export per tenant' on job_run.

Approach

  1. Name it: write skew. The two transactions read an overlapping set and write disjoint rows, so there is no row-level conflict for the engine to detect and each commit is individually legal.
  2. Rule out the levels precisely. READ COMMITTED takes a fresh snapshot per statement and takes no lock on the counted rows, so both see 49. PostgreSQL's REPEATABLE READ is snapshot isolation: it removes non-repeatable reads and phantoms within the snapshot but still admits write skew, because the anomaly is not a re-read of a changed row, it is a read of a set that a concurrent transaction invalidates. Only SERIALIZABLE closes it, by tracking the read dependency and aborting one transaction with SQLSTATE 40001 — a guarantee that exists only if the application re-runs the whole transaction from the read.
  3. Convert the set predicate into a single-row conflict: keep tenant.active_resource_count and run UPDATE tenant SET active_resource_count = active_resource_count + 1 WHERE tenant_id = $1 AND active_resource_count < 50 in the same transaction as the INSERT. Zero affected rows is the cap, returned as 409. The row lock serialises the decision at any isolation level, and contention is bounded to one tenant's row — which is also the fair-scheduling unit, unlike a global counter that would convoy every tenant behind one row.
  4. State the cost you just took on: a counter is a second source of truth that can drift, so every path that changes status must adjust it inside the same transaction, and a periodic reconciliation has to exist, with resource_revision as the authority for what the count should have been.

Follow-up

  • A resource moves from archived back to active. Which statements change, and what breaks if the counter update and the status change land in different transactions?
  • The cap becomes plan-dependent and a plan can change mid-month. Where does the number 50 live, and who reads it?

What are the primary differences between optimistic and pessimistic locking, and when would you use each in a

Medium · Core Software Engineering & Java

What are the primary differences between optimistic and pessimistic locking, and when would you use each in a distributed system?

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 an API that remains backward-compatible while undergoing significant underlying database sch

Medium · Core Software Engineering & Java

How do you design an API that remains backward-compatible while undergoing significant underlying database schema changes?

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?

Explain the pipeline architecture required to ingest, process, and store high-frequency signal data with minim

Medium · Systems & Signals Processing

Explain the pipeline architecture required to ingest, process, and store high-frequency signal data with minimal packet loss.

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 would you leverage GPU computing (using CUDA or OpenCL) to accelerate parallelizable data processing tasks

Medium · Systems & Signals Processing

How would you leverage GPU computing (using CUDA or OpenCL) to accelerate parallelizable data processing tasks compared to traditional CPU processing?

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?

Describe the architectural tradeoffs between using a relational database versus a NoSQL key-value store for st

Medium · Systems & Signals Processing

Describe the architectural tradeoffs between using a relational database versus a NoSQL key-value store for storing metadata generated by real-time sensor streams.

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 a highly available, multi-region cloud architecture that complies with strict federal securi

Medium · Cloud & Network Infrastructure

How do you design a highly available, multi-region cloud architecture that complies with strict federal security controls (e.g., ICD 503 or FedRAMP High)?

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 are the key differences between various routing protocols (such as BGP and OSPF), and how do you decide w

Medium · Cloud & Network Infrastructure

What are the key differences between various routing protocols (such as BGP and OSPF), and how do you decide which to implement in a hybrid cloud environment?

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?

Explain how you would implement automated infrastructure as code (IaC) using Terraform while maintaining stric

Medium · Cloud & Network Infrastructure

Explain how you would implement automated infrastructure as code (IaC) using Terraform while maintaining strict configuration drift detection.

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 configure secure, low-latency cross-domain solutions (CDS) to transfer data between networks of dif

Medium · Cloud & Network Infrastructure

How do you configure secure, low-latency cross-domain solutions (CDS) to transfer data between networks of different classification levels?

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?

Walk through the process of detecting and resolving a memory leak in a running production application.

Medium · Core Software Engineering & Java

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?

Walk us through how you would debug a latency spike in a distributed data pipeline processing gigabytes of dat

Medium · Systems & Signals Processing

Walk us through how you would debug a latency spike in a distributed data pipeline processing gigabytes of data per second.

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?

Describe the process of troubleshooting a routing loop in a complex, multi-site enterprise network.

Medium · Cloud & Network Infrastructure

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 Sunayu candidates report.

Day 1 — Map the Sunayu loop

  • Write out the reported sequence: Security Clearance Verification, Initial Screening, Technical Assessments, Comprehensive Panel Interview.
  • 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 4 reported rounds, with the weakest marked.

Day 2 — Work Secure Software Engineering

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

Deliverable: One timed worked example in Secure Software Engineering.

Day 3 — Work TS/SCI (Security Clearance Requirements)

  • Spend the session on TS/SCI (Security Clearance Requirements), which Sunayu candidates report being tested on.
  • Write one worked example in TS/SCI (Security Clearance Requirements) and time yourself on it.

Deliverable: One timed worked example in TS/SCI (Security Clearance Requirements).

Day 4 — Work Network Engineering

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

Deliverable: One timed worked example in Network Engineering.

Day 5 — Answer out loud: Core Software Engineering & Java

  • Answer aloud, timed: Describe how you would handle thread safety and synchronization in a high-throughput, multi-threaded Java application.
  • Answer aloud, timed: What are the primary differences between optimistic and pessimistic locking, and when would you use each in a distributed system?

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

Day 6 — Answer out loud: Systems & Signals Processing

  • Answer aloud, timed: Explain the pipeline architecture required to ingest, process, and store high-frequency signal data with minimal packet loss.
  • Answer aloud, timed: How would you leverage GPU computing (using CUDA or OpenCL) to accelerate parallelizable data processing tasks compared to traditional CPU processing?

Deliverable: Spoken answers to 2 reported Systems & Signals Processing question(s), under time.

Day 7 — Answer out loud: Cloud & Network Infrastructure

  • Answer aloud, timed: How do you design a highly available, multi-region cloud architecture that complies with strict federal security controls (e.g., ICD 503 or FedRAMP High)?
  • Answer aloud, timed: Describe the process of troubleshooting a routing loop in a complex, multi-site enterprise network.

Deliverable: Spoken answers to 2 reported Cloud & Network Infrastructure question(s), under time.

Behavioural preparation

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

Describe a time when you had to make a critical technical decision with incomplete information. What was the o

Medium · Behavioral & Mission Alignment

Describe a time when you had to make a critical technical decision with incomplete information. What was the outcome?

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 security regulations or compliance requirements conflict with development v

Medium · Behavioral & Mission Alignment

How do you handle situations where security regulations or compliance requirements conflict with development velocity or optimal system performance?

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?

Give an example of a time you had to explain a highly complex technical issue to a non-technical government st

Medium · Behavioral & Mission Alignment

Give an example of a time you had to explain a highly complex technical issue to a non-technical government stakeholder or customer.

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?

Tell us about a project failure you experienced. What did you learn, and how did you apply those lessons to su

Medium · Behavioral & Mission Alignment

Tell us about a project failure you experienced. What did you learn, and how did you apply those lessons to subsequent projects?

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 maintain focus, quality, and morale during long-term, highly structured projects with rigid regulat

Medium · Behavioral & Mission Alignment

How do you maintain focus, quality, and morale during long-term, highly structured projects with rigid regulatory milestones?

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?