Hire Site Reliability Engineers in London

Site Reliability Engineer specialist or generalist - which should you hire?

The honest answer depends on the half-life of your site reliability engineer surface area. If you expect to keep investing in SLOs and Observability work over the next 18-24 months, a specialist site reliability engineer will out-deliver a generalist on day-30 throughput and stakeholder confidence.

If your team is under ten people, or site reliability engineer responsibilities are spread across two or three roles already, hire a strong generalist who has shipped this work in anger at least twice. The cross-disciplinary pattern recognition will pay for itself the first time priorities collide.

On Haystack we surface both - filtered by whether the candidate self-identifies as a site reliability engineer specialist and verified against their last two roles. We benchmark live salary data on every offer.

What strong site reliability engineers actually bring

A great site reliability engineer is not the one with the longest CV - it is the one who has owned a hard SLOs call and changed how they work because of how it landed. Across the devops hires we have placed in 2025-2026, the same patterns keep showing up.

• Site Reliability Engineers who pair SLOs depth with cross-functional fluency - they bring product, design and data into their decisions, not just engineering.
• A written 30/60/90 plan in week one, anchored to Observability delivery milestones rather than ramp-up vanity metrics.
• An opinion on what NOT to do with SLOs, backed by an example where adding it would have hurt the team.
• Documented trade-off notes on the calls they made, including the option they rejected and why.

Red flags when interviewing site reliability engineers

Every discipline has its own pattern of plausible-sounding answers that fall apart in production. For site reliability engineers, these are the patterns that most often correlate with a six-month regret hire on the employer side.

• Treats the site reliability engineer role as a job title rather than a problem to solve - no opinion on what they would change about how the discipline is typically practised.
• Only ever worked on greenfield site reliability engineer projects - inheriting a messy, half-built system is a different muscle.
• Blames previous teams for failed SLOs work without explaining what they personally shipped to mitigate it.
• Cannot name a single site reliability engineer project where they removed scope rather than added it.

A sample take-home for site reliability engineer candidates

When teams ask us how to evaluate a site reliability engineer beyond a CV and a chat, we recommend a 90-minute paid take-home that mirrors real work, not a trivia quiz. The brief below is one we have refined with employers hiring across devops teams.

Give the candidate a small, intentionally imperfect artefact tied to "define and own slos and error budgets". Their task is to add a second capability - tied to "lead incident response and postmortems" - while keeping existing behaviour intact. Then grade in three parts.

• Correctness: the new work satisfies the brief and at least one edge case the candidate flags themselves.
• Judgement: did they refactor, wrap or work around the existing imperfection? Any of the three is fine - we are listening for the reasoning, not the verdict.
• Communication: a short written note explaining what they would do differently with another week, what they noticed about SLOs, Observability and Incident response, plus working exposure to Kubernetes, Prometheus and Grafana, and the assumptions they made along the way.

What to expect in the first 30 days from a Haystack site reliability engineer hire

By week one, the new site reliability engineer should have shipped a small, low-risk artefact to production or a stakeholder - a docs fix, a small process change, a first review on someone else's work. The goal is to validate the loop, not to ship anything heroic.

By week two, the site reliability engineer is shadowing the active workstreams, attending standups in observe-mode, and asking pointed questions about why specific decisions were made. If they are not asking those questions, the hire is going to plateau.

By day 30, they own one cleanly-scoped slice of the site reliability engineer surface area, have published a public ramp-up doc, and are the named point of contact for stakeholders inside that slice. Every Haystack employer gets a structured onboarding template, so you are not reinventing the playbook each hire.