Glossary
Infrastructure terms, in plain English
The acronyms and jargon you will meet when running infrastructure — explained without the gatekeeping.
- SLA
- Service Level Agreement — a written commitment to response and uptime targets, often backed by service credits if they are missed.
- Uptime
- The percentage of time a service is available. "99.9%" allows roughly 8.8 hours of downtime a year; "99.99%" allows under an hour.
- MTTR
- Mean Time To Resolve — the average time taken to fix an incident. Lower is better.
- RTO
- Recovery Time Objective — the maximum acceptable time to restore a service after a failure.
- RPO
- Recovery Point Objective — the maximum acceptable amount of data loss, measured in time (e.g. "up to 15 minutes").
- SPF
- Sender Policy Framework — a DNS record that lists which servers are allowed to send email for your domain.
- DKIM
- DomainKeys Identified Mail — a cryptographic signature that proves an email genuinely came from your domain and was not altered.
- DMARC
- A policy that tells receiving mail servers what to do with email that fails SPF and DKIM — and reports who is sending as you.
- Hardening
- Configuring a system to reduce its attack surface — closing unused services, enforcing good defaults, and applying security baselines.
- Patching
- Applying updates that fix security vulnerabilities and bugs. Unpatched systems are the most common way attackers get in.
- IaC
- Infrastructure as Code — defining your infrastructure in version-controlled files so it is repeatable, reviewable and rebuildable.
- FinOps
- The practice of managing and optimising cloud spend continuously, so cost is owned rather than left to grow.
- Observability
- The ability to understand what a system is doing from its outputs — logs, metrics and traces — especially when something goes wrong.
- Disaster recovery
- The plan and capability to restore your whole service after a major failure, with defined recovery targets and tested failover.
- P1–P4
- Priority levels for incidents, from P1 (critical, service down) to P4 (low, a request or question). They determine response times.
- On-call
- An engineer available outside normal hours to respond to urgent incidents — so problems are handled when they happen, not the next morning.
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