Crash Course: Interservice communication

From synchronous calls to Saga and eventual consistency.

Mentor - Kyrylo Melnychuk, CTO at AlterEGO and Uspacy

27 — 31 October 2026 Program

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Tickets cost from 6 200 UAH

Crash Course: Interservice communication

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Crash course: Inter-service communication — Fwdays

about the course

The crash course consists of 3 sessions of roughly 2 hours each. You will dive deep into one of the hardest topics in microservice architecture — how services actually talk to each other, how to keep data consistent without distributed transactions, and how to avoid the usual traps along the way.

Mentor: Kyrylo Melnychuk, CTO at Uspacy.

We will not be writing production code, but we will design communication schemes for real business scenarios in practice: from simple synchronous requests to full Saga orchestration with compensations. Every pattern comes with examples of anti-patterns — how NOT to do it and why.

By the end you will be able to:

choose between synchronous and asynchronous communication for a specific business scenario
design asynchronous flows with delivery guarantees (at-least-once, exactly-once)
implement Outbox, Idempotent Consumer and other reliable-delivery patterns
separate read and write models with CQRS where it is genuinely needed
coordinate distributed business operations through orchestrated and choreographed Sagas
understand what eventual consistency is and how to live with it in a product

format

Date and time27 and 29 October at 18:30, 31 October at 11:00

Duration3 sessions of ~2 hours (depending on the practice part)

Session formatLecture, Q&A, hands-on work in breakout rooms of 4–5 people — results reviewed at the end

PlatformZoom, the link is sent out the day before the course

PrerequisitesA basic understanding of microservice architecture (services, decomposition) — the course does not start from zero

Course languageUkrainian

Slides languageUkrainian with English terminology

Number of participantsLimited

audience

Developers from middle level and up
Team leads
Architects
Backend engineers who work with microservices or are preparing to move to them

program

Three sessions: from synchronous calls to Saga

NameTopicSession

session-1 Synchronous communication and the basics of asynchrony 27 Oct · 1/3 ›

– When and why services communicate synchronously; types of RPC (REST, gRPC, GraphQL) and their trade-offs
– Why a synchronous chain of calls is often an anti-pattern, and how to move to an asynchronous model through queues and message brokers
– Eventual consistency: how to explain it to a product manager and to a user
– Practice: an e-commerce scenario (order → stock deduction → loyalty points → email) — we design the synchronous and asynchronous versions and compare latency, fault tolerance and debugging complexity

session-2 Reliable message delivery 29 Oct · 2/3 ›

– Transactional Outbox: how to guarantee atomicity between a state change and publishing events
– Idempotent Consumer: why at-least-once delivery is the norm, and how to live with it
– CQRS: when it is genuinely needed and when it is premature optimisation
– Practice: an Outbox table, a consumer idempotency scheme (deduplication keys, storage) and a CQRS read model for the service from Session 1

session-3 Distributed business operations (Saga: orchestration vs choreography) 31 Oct · 3/3 ›

– Why 2PC and distributed transactions lead nowhere, and what Saga replaces them with
– Orchestrated Saga (with a central coordinator) vs choreographed Saga (through events)
– Compensating actions, error handling and Saga observability in production
– Real anti-patterns: choreography sprawl, an over-centralised orchestrator, missing timeouts
– Practice: a Saga for booking a trip (hotel + ticket + insurance + payment) — the orchestrated and choreographed versions compared on ease of debugging, scalability and risks

mentor

Kyrylo Melnychuk

CTO at Uspacy

– Co-founder and CTO @ Uspacy — a single workspace for small and medium businesses
– Co-founder and CTO @ AlterEGO — an IT integrator with 18 years of experience
– Loves automating everything that cannot be automated
– Builds processes and architectures
– Practises business-driven development
– LinkedIn
– Facebook