SLA

Availability is written as a percentage, and behind those percentages sit concrete minutes. 99.9% per month is roughly 43 minutes of downtime, 99.5% about 3.6 hours, 99% more than seven hours. The price gap between those tiers is a multiple, because every extra nine requires redundancy, monitoring and an on-call rota. Which leads to the practical question when choosing: what an hour of downtime costs your business specifically. For an online store in peak season it is lost revenue directly; for a corporate site usually not, and paying for 99.99% there buys nothing.

The second block is response and resolution, and conflating them is a mistake. Response time means the ticket has been accepted and work has begun; resolution time means the problem is fixed. A contract that fixes only response guarantees a polite reply in fifteen minutes and silence for three days. Both are set per severity class: critical (system unavailable or payments failing), high (a key journey broken with a workaround available), normal (an isolated defect), low (cosmetics and requests). The classification belongs in the contract, otherwise the argument about whether this counts as critical starts precisely when the outage does.

What to look at in the contract beyond the numbers. Support hours: 5x8 on business days and 24x7 are fundamentally different services at fundamentally different prices, and for a store a Saturday evening outage costs more than a Tuesday morning one. Exclusions: what does not count as downtime, such as planned maintenance, hosting or third-party failures, and the consequences of client-side changes. Measurement: without independent monitoring, availability is whatever the provider says it was. And compensation: without it an SLA is a statement of intent rather than an obligation, though expecting recovery of lost profit is unrealistic, since standard practice caps compensation at a share of the retainer.

Related terms

• CI/CDCI/CD is a pipeline that on every commit builds the project automatically, runs tests and checks, and then ships the passing build to a staging environment or to production, removing manual deployment and the human error that comes with it.
• Outsourcing vs in-houseOutsourcing and in-house are two ways to cover a development need: contract an external team at an agreed hourly rate, or build a staff team where salaries come with payroll taxes, recruitment, equipment and management on top.
• Fixed price vs time and materialsFixed price and time and materials are two contract models: the first fixes scope, deadline and price with the risk premium sitting on the contractor, while the second pays for hours actually worked at an agreed rate and leaves scope control with the client.
• APIAn API is a fixed set of rules by which one program requests data or actions from another: method addresses, request and response formats, authentication and rate limits, documented so that both sides can evolve independently.
• Technical debtTechnical debt is the accumulated gap between how a system is built and how it should have been built: every shortcut taken to hit a deadline turns into a permanent surcharge on the cost and duration of everything built afterwards.

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