Uptime monitoring in plain words

Reliability metrics

How availability and recovery are measured and promised.

• Uptime

  The time a service is available and working, usually as a percentage of a period. Read the definition : Uptime

• Downtime

  The time a service is unavailable or too broken to use. Read the definition : Downtime

• The nines (99.9% uptime)

  Nines of availability Availability targets counted in nines, from 99% to 99.999%, and the downtime each allows. Read the definition : The nines (99.9% uptime)

• SLA

  Service level agreement A contract that promises a service level, such as 99.9% uptime, and credits when it is missed. Read the definition : SLA

• SLO

  Service level objective An internal reliability target, with the error budget it leaves. Read the definition : SLO

• SLI

  Service level indicator The measurement behind an SLO: the share of good events. Read the definition : SLI

• MTTR

  Mean time to repair Mean time to repair, recover or resolve: how long failures last on average. Read the definition : MTTR

• MTTD

  Mean time to detect Mean time to detect: how long failures go unnoticed. Read the definition : MTTD

• MTBF

  Mean time between failures Mean time between failures: how often things break. Read the definition : MTBF

Incidents and alerting

What happens between something breaking and it working again.

• Incident

  An unplanned interruption that needs a response to restore service. Read the definition : Incident

• Postmortem

  Incident review A written review after an incident: what happened, why, and what changes. Read the definition : Postmortem

• Status page

  A public page that shows what works, so users don’t have to ask. Read the definition : Status page

• On-call

  A named person responsible for responding to alerts, in rotation. Read the definition : On-call

• Escalation policy

  Who gets alerted next, and when, if nobody responds. Read the definition : Escalation policy

• Alert fatigue

  Too many alerts, so the important ones get ignored. Read the definition : Alert fatigue

• Maintenance window

  A scheduled period for planned work, with alerts paused on purpose. Read the definition : Maintenance window

• False positive

  An alert about a problem that isn’t there. Read the definition : False positive

Types of monitoring

The ways to find out that something stopped working.

• Synthetic monitoring

  Scripted checks from outside, on a schedule, with or without real traffic. Read the definition : Synthetic monitoring

• Real user monitoring (RUM)

  RUM Performance measured from actual visitors’ browsers. Read the definition : Real user monitoring (RUM)

• Heartbeat monitoring

  Cron job monitoring Jobs ping a URL when they run; a missing ping is the alert. Read the definition : Heartbeat monitoring

• Keyword monitoring

  Checks that a page shows the right text, not just that it answers. Read the definition : Keyword monitoring

• API monitoring

  Real requests to API endpoints, checked for status, data and speed. Read the definition : API monitoring

• Ping (ICMP)

  ICMP echo requests that show a host is reachable, and how fast. Read the definition : Ping (ICMP)

• Port monitoring

  Checks that a service accepts TCP connections on its port. Read the definition : Port monitoring

Speed and HTTP

How fast a service answers, and what the answer means.

• HTTP status codes

  The three-digit answer to every request: 2xx success to 5xx server error. Read the definition : HTTP status codes

• Response time

  How long a request takes, from sending it to the full answer. Read the definition : Response time

• TTFB

  Time to first byte Time to first byte: how quickly the server starts answering. Read the definition : TTFB

• Latency

  The network delay between two points, as round-trip time. Read the definition : Latency

Domains, DNS, email and certificates

The parts outside your server that take a site down when they expire or change.

• SSL/TLS certificate expiry

  The date a certificate stops being valid and browsers warn visitors. Read the definition : SSL/TLS certificate expiry

• Domain expiry

  The date a domain registration runs out, taking site and email with it. Read the definition : Domain expiry

• DNS propagation

  The wait before a DNS change is seen everywhere, set by TTLs. Read the definition : DNS propagation

• DNS record types

  A, AAAA, CNAME, MX, TXT, NS, SOA, CAA: what each DNS record holds. Read the definition : DNS record types

• SPF, DKIM and DMARC

  The DNS records that prove mail really comes from your domain. Read the definition : SPF, DKIM and DMARC

All terms A–Z

• Alert fatigue
• API monitoring
• DNS propagation
• DNS record types
• Domain expiry
• Downtime
• Escalation policy
• False positive
• Heartbeat monitoring
• HTTP status codes
• Incident
• Keyword monitoring
• Latency
• Maintenance window
• MTBF
• MTTD
• MTTR
• On-call
• Ping (ICMP)
• Port monitoring
• Postmortem
• Real user monitoring (RUM)
• Response time
• SLA
• SLI
• SLO
• SPF, DKIM and DMARC
• SSL/TLS certificate expiry
• Status page
• Synthetic monitoring
• The nines (99.9% uptime)
• TTFB
• Uptime

Want to try the numbers? The free tools turn uptime targets into downtime, read cron schedules and check certificates, DNS and email records. The blog goes deeper on each topic.