Backend Engineer | Senior | Transition to Go | Saily

Nord Security; Poland; Hybrid; PLN 180,000 - 260,000; Full time

Benefits offered by this job

Training and mentorship program

Extra vacation and sick days

Private health insurance in Lithuania/

Calm/Headspace/Mindletic subscriptions

In-house gyms and sport cards

Workation trips

Remote work flexibility

Milestone celebrations gifts

Parental support and camps for kids

Team-building events

Vilnius HQ amenities

Job summary

Saily is building a new eSim product with an AI-native engineering culture. The backend engineer will design scalable microservices, implement personalization layers, and contribute to analytics while maintaining high-quality code.

You will work with Go, SQL/NoSQL databases, Kafka, and Kubernetes in a cross-functional team, shaping the product from idea to production and exploring AI-assisted optimization.

Qualifications

• Over 4 years of experience in backend development.
• Experience with PHP, Python, C#/.NET, Java, or Kotlin.
• System design is familiar; know patterns to use, when, and why.
• K8s and microservice architecture experience is a plus.
• Experience with SQL (MySQL, PostgreSQL) and NoSQL (Cassandra, Redis).
• Experience with Kafka.
• Strong API design mindset: APIs that are easy to use and understand.
• Curious about AI and excited to work with agents.

Responsibilities

• Build a completely new sophisticated microservices system for the new eSim Product.
• Create features to support layers of multi-dimensional personalization, A/B experimentation, and analytics.
• Develop and maintain a high-quality codebase.
• Seek to improve code and performance constantly.
• Mentor colleagues on development best practices & provide technical guidance.
• Exercise influence on the overall vision and long-range goals of your team.
• Perform R&D operations whenever required.
• Use AI agents for specifications, coding, analysis, testing, and iteration.
• Work as part of a cross-functional team and help to ensure smooth communication between all team members.
• Collaborate with engineering, product, and design professionals from other teams.

Skills

Go

System design

APIs

Microservices

AI curiosity

Tools

Go

MySQL

Kafka

Kubernetes

AWS

Redis

Copilot Cursor

Job description

At Saily, we’re removing the hassle of staying connected while traveling — no roaming fees, no plastic SIM cards, just lightning-fast, secure mobile data in 200+ destinations. Saily has millions of paying customers and hundreds of thousands travelers browsing through Saily at any given moment.

To build the best product for our customers we foster AI-native Product Engineering culture, where:

- The Engineer is the builder, who is responsible for solving customer problems end-to-end (idea to production)
- AI Agents are the enablers who write most of the code and solve repeatable tasks to help the Engineers maximize their impact
- Everyone contributes to making Saily effective by suggesting new areas for improvement to delegate to agents and then implementing the changes
- Curiosity, learning and sharing are everyone's responsibility
- Customer, having a comfortable, connected, hassle-free journey is never lost from the focus

We value growth over comfort, contribution over hierarchy, and impact over process. At Saily, we believe in giving sharp people context, autonomy, and AI as their multiplier to allow them to just do their best work.

Main Responsibilities

• Build a completely new sophisticated microservices system for the new eSim Product

• Create features to support layers of multi-dimensional personalization, A/B experimentation, and analytics.

• Develop and maintain a high-quality codebase

• Seek to improve code and performance constantly

• Mentor colleagues on development best practices & provide technical guidance

• Exercise influence on the overall vision and long-range goals of your team

• Perform R&D operations whenever required

• Use AI agents for specifications, coding, analysis, testing, and iteration

• Work as part of a cross-functional team and help to ensure smooth communication between all team members

• Collaborate with engineering, product, and design professionals from other teams

Core Requirements

• Over 4 years of experience in backend development.

• Experience working with any of the following backend languages: PHP, Python, C#/.NET, Java, Kotlin

• System design is nothing new to you, and you know what patterns to use, when, and why

• Previous experience in working with K8s and microservice architecture is a plus

• Previous experience with SQL (MySQL, PostgreSQL) and NoSQL (Cassandra, Redis) solutions

• Previous experience with Kafka

• Passionate about building APIs that are easy to use and simple to understand

• Strong product mindset: focus on problems, outcomes, and impact—not just tickets or tasks

• You are curious about AI and excited to work with agents

Tools You Will Use

• Go

• MySQL

• Kafka

• Kubernetes

• AWS

• Redis

• AI tools like Copilot Cursor

What We Offer

• Sharpen your edge: training, mentorship, and room to grow — always.

• Take the time you need: extra vacation days, sick days, and time off when life calls.

• Get premium healthcare: private health insurance in Lithuania and Poland — fully covered.

• Protect your peace: enjoy free subscriptions to Calm, Headspace, and Mindletic, and our own resilience and mindfulness trainings.

• Own your fitness: in-house gyms, sport cards, online workouts, and personal guidance — on us.

• Pack your bags for workation: experience our company-wide trip abroad to the fullest.

• Work from anywhere: work from wherever keeps you in the zone.

• Celebrate your milestones: birthdays, weddings, and new family members — all deserve a gift.

• Parent with ease: children’s summer camps and flexibility around the schedule — because parenting never pauses.

• Join the party: team building and company events people talk about for months.

• Unlock Cyber City: coffee bar, open gyms, kids’ room, music room, massage chairs — our Vilnius HQ is yours to enjoy.

Kindly refer to our Privacy Notice for Recruitment Candidates for comprehensive information regarding our data handling procedures throughout recruitment processes.

We expect all candidates to provide accurate and complete information during the recruitment process. While limited use of AI tools to refine application materials is acceptable, candidates remain fully responsible for ensuring that their submissions reflect their own qualifications, skills, and experience. Any failure to do so may negatively affect participation in the recruitment process. If broader AI assistance is allowed for a particular role or stage, we’ll let you know in advance.

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If you would like more information about how AI is used in this process or wish to exercise your rights under applicable data privacy laws, please contact us at [e-mail]. Should you prefer to opt out of the automated evaluation, please submit your application directly to [e-mail].