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Backend Engineer

Cossack Labs
format:Hybridcompany:Product
gopythonbashpostgresqlmysqlsqldockergrpcprotobufwebsockets
rustccryptographytlslinux
semantic dedup

Reposted 2× across DOU — deduped to one listing.

metahunt matched 2 postings of this exact role by semantic similarity, so you see it once instead of 2 times.

test task:yes
englishB2
experience3+ years
domainCyberSec
locationUkraine (Kyiv, Lviv)
> full description

This position is open only to candidates currently residing in Ukraine (preferably in Kyiv or Lviv).

Our product team is looking for an experienced Golang developer. You’ll help create robust, mission‑critical systems. We’re primarily looking for mid-level specialists. However, if you’re more senior and have a background in cryptography, security, or systems programming, we’d be happy to talk.

Technical stack:

  • Golang for product development, Python for tests.
  • Protobuf/gRPC, WebSockets.
  • OS: Linux Debian (mostly). Alpine, other distributives just for Docker images and test environments.
  • DB: PostgreSQL, MySQL/MariaDB, Redis.
  • CI/CD: GitHub, CircleCI, Buildbot.

You will:

  • Take part in feature discussions and influence architecture/design decisions.
  • Build and ship new features in our core infrastructure products.
  • Write unit and integration tests.
  • Document new functionality clearly and concisely.
  • Share implementation examples for other engineers.
  • Contribute to code reviews, design sessions, and test case design.

Requirements:

  • Strong knowledge of Go (3+ years): syntax, idioms, and common patterns.
  • Solid understanding of engineering fundamentals including algorithms, concurrency, multithreading, data structures, design patterns, networks.
  • Comfortable working with Python and Bash to read, write, and maintain scripts.
  • Experience with PostgreSQL or MySQL/MariaDB: basic knowledge of SQL and practical experience with DBMS (at least one of them)
  • Practical knowledge of Docker: writing Dockerfiles, working with images/containers.
  • Confident debugging skills: practical experience in diagnosing problems at any level (application, network, server, database, OS).
  • Background in computer science.
  • Good spoken and written English (B2+) for team communication and code documentation.

Nice to have:

  • Rust/C: some of our products written with C/Rust. It would help your work if you’re able to read/maintain/review code in Rust/C.
  • Security & cryptography: basics of information security, symmetric/asymmetric cryptography, TLS.
  • Linux: understand how application communicates with OS, difference between userspace & kernelspace, how to deal with blocking operations.

Hiring Process

  • Resume review — up to 7 business days.
  • Test task — estimated time 3-4 hours.
  • Introductory meeting with the Head of development & solution engineering.
  • Technical interview with several team members.
  • Background check.
  • Offer discussion.

What to expect from us

  • We build applications for clients, write code for developers, and document how it all works — for both.
  • Everyone on the team is happy to help, but we also respect each other’s time and know how to find answers ourselves.
  • Tech writing isn’t our favourite task, but we do create solid technical documentation when needed, and we’re lucky to have a tech writer to help with that.
  • We prefer doing things right the first time over patching things endlessly later.
  • We value healthy perfectionism, a sense of beauty in engineering, and a good sense of humour.

What’s in it for you?

  • Competitive compensation with a flexible and clear bonus scheme
  • Paid vacation — 21 business days per calendar year
  • Paid sick leaves
  • Hybrid work model: this position allows for a combination of in-office and remote work as needed
  • Combining technologies: hardware engineering, software engineering, cryptography, information security
  • You will work with people deeply interested in security engineering, you will learn a lot
  • Reasonable time budgets and an attitude to build things well — we prioritise building for decades, rather than just until the next release
  • Conferences, books, courses — we encourage learning and sharing with the community. Our team members share a a lot in talks, workshops, and blog posts
  • Public track record in the open-source aspect of our products.

At our company we engineer and deploy end‑to‑end solutions for the world’s most critical infrastructure—both defense systems and power grid operations. Working side‑by‑side with operators, vendors, and manufacturers from Ukrainian to global dual‑use firms, we guide projects from initial design through field deployment, ensuring that OT and IT environments are fully hardened against targeted cyber and physical attacks. In every engagement the stakes are tangible: a failure means blackouts or mission loss rather than just an SLA violation.

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