Incident Post-Mortems
Learn from incidents, understand root causes, document what happened and make systems better for the future.
01. What is a Post-Mortem?
An incident post-mortem is a report written after an incident or outage has been resolved. It documents what happened, why it happened, how it was handled and what can be improved.
The main objective is not to find someone to blame. Instead, the goal is to learn from mistakes and make the organization’s systems, processes and response procedures more reliable.
02. Why Are Post-Mortems Important?
Every IT environment can experience unexpected problems. Servers crash, networks fail, configurations break and applications become unavailable.
A post-mortem allows an organization to investigate these incidents instead of simply fixing the immediate problem and moving on.
Important: Blameless Culture
A post-mortem should be honest but not focused on blaming or shaming individuals.
Instead of asking “Who made the mistake?”, ask “Why did the system allow this mistake to happen?”
03. What Goes Into a Post-Mortem?
A typical incident post-mortem contains several important sections. Each section provides a different piece of the incident investigation.
Incident Summary
The summary is a brief paragraph at the beginning of the report. It gives readers a quick understanding of what happened without requiring them to read the entire report.
It should include:
- What was the incident?
- How long did it last?
- What was the impact?
- How was it fixed?
Detailed Timeline
The timeline records important events in the order they occurred. It should include what happened, when it happened and who was involved.
- When did the incident begin?
- When was it detected?
- When were team members notified?
- What actions were taken?
- When were services restored?
Always include the correct date, time and time zone. This is especially important when teams operate in different countries.
Root Cause Analysis
The root cause explains the underlying reason an incident occurred. It should be detailed and honest.
Common examples:
- A configuration change was deployed without proper testing.
- A command was typed incorrectly.
- A monitoring system failed to detect an issue.
- A server ran out of storage space.
- A network component failed unexpectedly.
The important thing is to identify why the mistake was possible and what can be changed to prevent it.
Resolution and Recovery Details
This section describes the recovery process in more detail than the timeline.
It should explain which actions were performed, why those actions were chosen and what the outcome of each action was.
- What recovery steps were performed?
- Why were those steps selected?
- What happened after each step?
- How was successful recovery verified?
Future Improvements and Action Items
The final section lists specific improvements that should be considered or implemented. It can include improvements to prevention, detection and incident response.
Examples:
- Introduce mandatory testing before deploying changes.
- Improve monitoring and alert notifications.
- Automate error-prone manual processes.
- Improve incident response documentation.
- Introduce additional verification steps.
- Improve failover and backup procedures.
04. Timeline vs. Detailed Analysis
This distinction is particularly important for exams. Both sections discuss the incident, but they serve different purposes.
Timeline
Focuses on WHEN something happened and WHAT action was taken.
09:10 UTC – IT team begins investigation.
Detailed Analysis
Focuses on WHY something happened, HOW it was fixed and WHY specific recovery actions were selected.
05. What Went Well?
One commonly overlooked part of post-mortems is documenting what actually went well during an incident.
A post-mortem should not only focus on failures. It should also identify systems and procedures that worked as intended.
Examples of things that went well
- A backup server successfully took over.
- A redundant internet connection prevented a complete network outage.
- Monitoring detected the problem quickly.
- The IT team responded quickly and communicated effectively.
- Backups allowed data to be restored successfully.
Documenting this success demonstrates the value of investing in redundant systems and preventative measures.
06. Sharing the Post-Mortem
Writing the report is not necessarily the final step. It should also be shared with relevant people in the organization.
Sharing post-mortems helps different teams learn from incidents, recognize risks and improve their own systems and procedures.
When teams openly discuss mistakes and successes, the entire organization benefits from the experience.
07. Complete Example: Application Outage
Let’s combine everything into one realistic scenario.
A company’s website goes offline
Incident summary
A website became unavailable for 45 minutes after an incorrect firewall configuration was deployed. The IT team restored the previous configuration and verified that the website was accessible again.
Root cause
A firewall rule was deployed without being tested in a staging environment. It blocked traffic required by the website.
Resolution
The team rolled back the firewall configuration and tested the website to confirm that services were working again.
What went well
Monitoring detected the outage quickly, and the IT team responded within minutes.
Future improvements
- Require firewall changes to be tested before deployment.
- Improve monitoring alerts.
- Document rollback procedures.
- Introduce automated configuration validation.
08. Exam Cheat Sheet
| Section | What to remember |
|---|---|
| Summary | What happened, duration, impact and fix. |
| Timeline | Events, actions, dates, times and time zones. |
| Root Cause | Why the incident happened. |
| Resolution | How it was fixed and why. |
| Improvements | How to prevent or respond better next time. |
| What went well | Successful systems and response actions. |
| Sharing | Help other teams learn from the incident. |
The golden rule
Own the mistakes, understand the causes, recognize what worked and make things better for the future.
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