At a glance
What you need to know.
To maintain an agreed user journey as volume, dependencies and failure exposure increase, start with a complete business journey and its operating constraint. This guide examines a SaaS service coexisting with an established ERP, then connects the design choice to an observable result. The walkthrough is illustrative guidance; targets, access and readiness must be established for the actual system.
Start with a SaaS service coexisting with an established ERP
Introducing a SaaS workflow beside a legacy ERP creates an authority boundary. Decide whether the SaaS service proposes changes, owns new records or mirrors established ones. Preserve the ERP's business identifiers and validation rules during coexistence. A browser-based interface can simplify access, but it must not become an unreviewed second source of truth. Inventory scheduled exports and downstream reports before migrating the workflow. Users need to see whether a change is local, approved for transfer or accepted by the authoritative destination.
A legacy estate is an active business system, not merely old code. Locate scheduled jobs, shared files, identifiers and approvals that users rely on before replacing a component. Some dependencies appear only at a month-end or exceptional transaction. Establish a way to compare old and new results using stable business references. Where systems coexist, decide which one owns each write and how conflicts are reconciled. A temporary bridge needs a removal condition and an owner, otherwise it becomes another permanent dependency.
Choose the saas platforms boundary that changes the result
Separate the availability of the shared platform from the successful journey of each tenant. One large customer can exhaust connection, worker or queue capacity while the global success rate looks acceptable. Segment indicators and establish workload limits before adding replicas. Make provisioning and migrations recoverable independently from product reads. Decide which capability can degrade safely when a dependency fails. Test tenant-specific configuration and data size as well as a clean demonstration account; reliability is a property of the operated service and its workload.
Resolve the decision within this operating context
Rehearse the new boundary and the old destination together, including a missed batch, unavailable interface and partial transfer. Keep writes owned by one system or an explicit reconciliation contract during coexistence. Define a fallback that does not silently create competing records. Decide when to cut over based on destination-state evidence and restoration capability. A successful new endpoint is insufficient when an essential legacy job still fails after the request is acknowledged.
Illustrative walkthrough and failure case
Exercise a customer account change synchronized to the ERP while its most important dependency is slow or unavailable. Choose the write authority for each field and the reconciliation rule for changes made while the two systems coexist. Record the user-visible pending state and inspect durable progress after recovery. Test with the workload that creates contention, rather than only an empty demonstration account, and compare the useful result with the agreed objective.
A legacy export arrives after a newer approved SaaS correction. Use source version and agreed precedence to detect the conflict; blind last-arrival wins can silently restore the obsolete value.
Define the acceptance metric before the pilot
Define a service-level indicator around a useful user journey: accepted request, successful retrieval or durable completed job. Specify eligible events, success conditions and the measurement window. Review latency percentiles and failures by customer or workload class, not only a global average. Agree an objective with the business owner based on consequences and operating capacity. Google SRE distinguishes the measured indicator from the target objective; a provider's availability commitment does not automatically describe your application or its downstream dependencies.
Exercise slow and unavailable dependencies, duplicate work, restart and restoration under a representative load. Confirm timeouts and retries are bounded, work remains traceable and the interface represents pending or degraded state honestly. Test recovery using the actual data and permissions required by the journey. Compare failure and latency indicators with the agreed objective before expanding rollout. Scaling instances proves capacity only for the tested workload; it does not prove recovery from corrupt data, an invalid release or a missing authority service.
Release a supported change and retain ownership
Release the change to a bounded tenant or workload group with a documented configuration and data boundary. Keep tenant identity server-derived and test background jobs, exports and caches with the same scope as interactive requests. Define who handles a failed provisioning or migration before opening the feature to more customers. Record support capacity and any account-plan limits. A SaaS release is complete only when the intended tenant can perform the journey and another tenant cannot gain access through identifiers, shared state or a support shortcut.
Before you start.
- What useful user result does the reliability objective measure?
- Choose the write authority for each field and the reconciliation rule for changes made while the two systems coexist.
- Which restricted role, correction and dependency failure belong in acceptance?
- Who owns unfinished work and reconciliation during the pilot?
- Which baseline, workload assumptions and stop condition are recorded?
Common questions.
How should we measure scaling reliability?
Define the user journey, eligible events and success rule first. Set an objective that reflects business impact and the team's ability to operate it. Measure dependency failures and recovery as well as healthy requests; a fixed-success health endpoint cannot establish journey reliability.
What should the first pilot cover for a SaaS service coexisting with an established ERP?
Use one bounded journey involving a customer account change synchronized to the ERP, with its actual authority, source records and operating owner. Choose the write authority for each field and the reconciliation rule for changes made while the two systems coexist. Include the failure case and confirm accepted destination state before expanding. A successful screen or resource-creation receipt is evidence of that stage, not proof that the full journey is ready.