Objectives (SLO)

“The site is 99.9% available” is a promise made to a client, a boss, oneself. The Objectives page (Project → Operations → Objectives) measures it: what is observed, how much margin is left, how fast it melts, and — month by month — whether the promise was kept.

What PostShip does

Two kinds of objectives

• Availability: the share of successful passes, on the whole project (its pages, journeys and APIs) or on one URL. Suggested targets: 99%, 99.5%, 99.9%, 99.95%, 99.99%.
• Latency: 95% of successful responses under a target — 300, 500, 800, 1,200 or 2,000 ms. A failing pass counts as a response that is too slow.

A pass is a page check (HTTP, journey, API contract); site checks and certificates do not count. Up to twelve objectives per project.

The error budget

Over thirty rolling days, the target tolerates a number of bad passes: 0.1% of 8,640 passes is 8. The error budget is that tolerance; the bar says how much of it is consumed — green under half, orange beyond, red when exhausted.

The burn rate

What the last 24 hours consumed, relative to what a “normal” day should consume for the budget to last exactly the window. At 1, you are just holding; at 2, the budget will be dry in a fortnight; at 0, nothing was lost. It is the number to look at on the morning of an incident: it says whether you can afford to wait.

The report by month

Each past day is summed up — passes, failures, slow responses, p95 — in a table that survives the purge of checks (fourteen or thirty days depending on the plan). The report lines up the months: observed, target, met or missed. When an objective is created, the past still in the database is picked up right away.

Settings

On the page: the scope (the whole project, or a URL), the type, the target, “Add”. “Remove” deletes the objective and its sums. The Overview's error budget remains the quick view of the project's global objective.

What triggers an alert

No new alert: incidents already alert. Objectives are there to read the margin and be accountable.

Limits and plans

See plans.

Troubleshooting

The budget says “none tolerated”

With few passes, 0.1% is less than one pass: the first failure exhausts the budget. That is arithmetic; the reading becomes fair after a few days of measurements.

The current month says “met” but the 30-day window says “missed”

The two do not look at the same thing: the month counts from the 1st, the window from thirty days back. An incident at the end of last month weighs on the window, not on the month.

Latency is missed although the median is good

95% of responses must hold the target: a page fast on average but slow one time in ten misses the objective — which is what one visitor in ten experiences.