What is an ESB (Enterprise Service Bus)?

ESB (Enterprise Service Bus) is the coordination layer many organisations use to make diverse systems work as one: handling messaging, routing, transformation, and orchestration between legacy apps, cloud services, and shop-floor systems. 

In this guide, we’ll explore how ESBs work, where they help (and hurt), how they compare with iPaaS and event-driven architectures, and when to modernise or keep them in place.

What is an ESB?

An ESB, or Enterprise Service Bus, is a middleware layer that lets otherwise incompatible systems talk to each other through a common “bus.” Instead of every application integrating directly with every other, each connects once to the bus via adapters. 

The ESB then handles message translation, routing, security, and reliability, so your ERP, MES, SCADA/PLC gateways, WMS/TMS, and cloud services can exchange data and trigger processes without point-to-point spaghetti.

How does an ESB work?

Applications publish requests or events to the bus using their native protocols (HTTP/SOAP/REST, JMS/MQ, SFTP, etc.). The ESB’s mediation layer normalises those messages to a canonical model, applies transformations and validations, and enforces policies like authentication, rate limits, and schema checks. 

A routing engine directs each message, content-based or rules-driven, to the right downstream services, and can orchestrate multi-step flows (for example: receive a purchase order, enrich with master data, split by plant, then fan out to MES and supplier portals). 

Under the hood, durable queues and topics decouple senders from receivers, retries and dead-letter handling protect against failures, and monitoring/tracing provide end-to-end visibility. The result is a dependable, governed backbone that supports both request/response and publish/subscribe patterns, making large engineering, technical, and industrial environments easier to scale and change.

ESB vs SOA

SOA (Service-Oriented Architecture) is an architectural style: you model business capabilities as independent services with clear contracts, loose coupling, and governance (registries, policies, SLAs). It’s a way of organising systems.

ESB (Enterprise Service Bus) is middleware: a product/pattern that implements parts of SOA by mediating traffic between services, handling routing, transformation, protocol bridging, security, and orchestration. It’s one way (not the only way) to realise SOA.

In practice, you can do SOA without an ESB (e.g., lightweight REST services behind an API gateway plus a message broker), and you can use an ESB outside a “pure” SOA to connect legacy systems (ERP, MES, SCADA/PLC gateways, WMS/TMS) via adapters. 

The trade-off is centralisation vs. autonomy: ESBs concentrate mediation and control, which simplifies governance but can become a bottleneck (“smart bus, dumb endpoints”). Modern SOA leans the other way (“smart endpoints, dumb pipes”) using API gateways, event streams, and service meshes so each service owns more logic and scales independently.

Rule of thumb: keep or adopt an ESB where you must bridge diverse, legacy protocols and enforce canonical data models at scale (common in large engineering, technical, and industrial estates). Prefer a lighter SOA with API gateways + event/messaging for greenfield and microservices: faster to evolve, easier to scale, and less risk of a central choke point. Many mature environments run a hybrid: ESB for hard-to-replace integrations; API-led and event-driven patterns for new work.

ESB and microservices

Microservices favour autonomy: small, independently deployable services with “smart endpoints, dumb pipes.” An ESB centralises mediation (routing, transformation, orchestration), which can become a control point and, if overused, a bottleneck. That’s why dropping a traditional ESB into a microservices core is usually an anti-pattern: it couples teams to a shared runtime, slows releases, and hides business logic in the middle.

Where an ESB does help is at the edge of your microservices estate, acting as an anti-corruption layer to legacy systems. In engineering, technical, and industrial environments, the ESB can bridge protocols (SOAP, file, EDI, OFTP2), normalise canonical data from ERP/MES/SCADA gateways, and expose clean REST or event contracts to your services. Keep this boundary thin and purpose-built, protocol bridging and coarse transforms only, so internal services stay decoupled.

Inside the microservices layer, prefer API gateways + messaging/streaming and, when needed, service mesh for cross-cutting concerns (authN/Z, retries, mTLS, observability). Use events (choreography) for loosely coupled flows; if you truly need orchestration, place it in a dedicated domain service or workflow engine rather than the ESB. This preserves team ownership and keeps latency and failure domains local.

For modernisation, a strangler-fig approach works well: sit the ESB in front of the monolith/legacy, route traffic through new microservices as they’re carved out, then gradually retire mappings on the bus. Throughout, enforce contracts (OpenAPI/AsyncAPI), versioning, idempotency, and tracing so you maintain the velocity microservices promise without losing the reliability your plants and supply chain demand.

Where nocode tools fit with ESB functionality 

These platforms don’t replace an ESB or microservices; they wrap and extend them. Use them at the edge for human-in-the-loop tasks, long-tail automations, partner onboarding, and back-office updates without touching your core bus or services.

Here are a few examples.

Zapier. Fast, business-friendly orchestration around your API/EDI/ESB events (webhooks in, actions out). Great for alerts, approvals, light transformations, and syncing records between SaaS apps. We specialise in designing robust, governed Zaps with retries, idempotency, and audit trails.

Make. Visual flows with routers, iterators, and granular control. Ideal when you need more complex branching logic, multi-step enrichments, or hybrid API + file automations alongside the ESB.

n8n. Open-source and self-hostable for data residency and custom nodes. Useful when you want iPaaS flexibility with on-prem control; e.g., running near plant networks or inside a private cloud.

Airtable. A lightweight operational data store and “control tower” for exceptions, cases, and partner onboarding. Non-technical teams can triage, fix, and approve changes that your ESB/APIs then apply.

Xano. A nocode backend to expose clean REST APIs and perform server-side transforms. Handy as an anti-corruption layer in front of legacy systems or to stand up partner-facing endpoints quickly.

Good pattern: ESB or services publish webhooks/events → iPaaS catches, enriches, and notifies → writes back via APIs (with guardrails: rate limits, idempotency keys, error queues). Reserve the ESB for canonical, high-throughput flows; use these tools for agile, lower-risk automations that keep people and partners in the loop.

How flowmondo assists with software integration 

Where it helps, we pair core services with iPaaS and nocode tools: Zapier for agile orchestration, Make or n8n for complex branching, Airtable for exception “control towers,” and Xano to expose clean partner APIs. Using a strangler-fig approach, we wrap legacy, route traffic to new services as they land, and retire risk bit by bit, maintaining uptime while you modernise.

If you’re consolidating integrations, moving to event-driven patterns, or building a partner API program, we’ll help you choose the right architecture and ship it safely. For the broader picture, see our main guide: [Software Integration for Modern Businesses].

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