Implementing Site Reliability Engineering Practices for a High-Traffic FinTech API

Key Results

  • 85% Faster MTTR
  • 99.95% SLO Achieved
  • Zero Repeat Incidents
  • 4x On-Call Reduction

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Project Background

A UK FinTech processing over £4 million in daily payment transactions was experiencing an average of three production incidents per week. Their on-call rotation had become unsustainable — engineers were burning out, incidents had no post-mortems, and the same failures recurred monthly. Leadership needed a structured approach to reliability before a major bank partnership launch.

The Challenge

We were engaged to introduce SRE discipline across a 12-person engineering team with no prior SRE experience. The mandate included defining service level objectives, building the tooling to measure them, restructuring the on-call process, and running the first chaos engineering experiments on a system where downtime directly impacts regulated financial transactions.

What We Delivered

  • Facilitated SLO definition workshops to establish 99.95% availability and p99 latency targets for the payment API and webhook delivery service
  • Instrumented the full request path with OpenTelemetry, feeding traces into Grafana Tempo and metrics into Prometheus with pre-built SLO dashboards
  • Implemented multi-window, multi-burn-rate alerting that pages only when the error budget is being consumed faster than sustainable — reducing alert noise by 70%
  • Rebuilt the incident management process: severity taxonomy, runbooks per alert, mandatory blameless post-mortems with action-item tracking in Linear
  • Introduced Chaos Monkey-style experiments using AWS Fault Injection Simulator (FIS) to validate resilience before the bank partnership launch
  • Embedded two OpsNexus engineers with the team for 8 weeks to transfer SRE knowledge and establish the on-call rotation

Technical Stack

Observability: OpenTelemetry · Prometheus · Grafana · Grafana Tempo · Alerting: Alertmanager · PagerDuty · Chaos: AWS Fault Injection Simulator · Incident Mgmt: Linear · Notion runbooks

Outcomes

Mean time to recovery dropped from 47 minutes to under 7 minutes. The team went from 3 incidents per week to fewer than one per month, with zero repeat incidents in the first quarter post-engagement. On-call pages dropped by 75%, and the bank partnership launched on time with the reliability commitment backed by six weeks of SLO data. The engineering team now runs SRE practices independently.