Troubleshooting · Lesson 13 of 26 · 8 minutes

Incident bad deploy

Compare configs and hash scripts during deploy triage.

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Your objectives

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1
Compare configs
Run diff data/config-a.conf data/config-b.conf.
Hint & worked example
Compare two text files; a difference is a meaningful nonzero status, not necessarily an execution error.
Inspect the differences. diff exits 1 when files differ and 0 when they match.
```
diff data/config-a.conf data/config-b.conf
```
Remember: Status 1 means differences for diff; shell status must be interpreted in command context.
2
Hash deploy
Run sha256sum scripts/deploy.sh.
Hint & worked example
Compare content digests to detect byte changes, not to establish who authored the file.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
sha256sum scripts/deploy.sh
```
Remember: A checksum detects changes only relative to a trusted expected digest.
3
Validate nginx
Run nginx -t.
Hint & worked example
Check the simulated configuration using nginx -t before changing service state.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
nginx -t
```
Remember: This lab checks a limited configuration subset, not the complete Nginx parser.

Understand the pattern

Junior operators build confidence by gathering evidence before changing systems.

diff: Compare two text files; a difference is a meaningful nonzero status, not necessarily an execution error.
Status 1 means differences for diff; shell status must be interpreted in command context.
sha256sum: Compare content digests to detect byte changes, not to establish who authored the file.
A checksum detects changes only relative to a trusted expected digest.
nginx: Check the simulated configuration using nginx -t before changing service state.
This lab checks a limited configuration subset, not the complete Nginx parser.

Worked example and expected result

$ diff data/config-a.conf data/config-b.conf

--- /home/learner/data/config-a.conf
+++ /home/learner/data/config-b.conf
-listen 443 ssl;
+listen 8443 ssl;

Exit status: 1. This nonzero result is an expected part of this exercise.

$ sha256sum scripts/deploy.sh

f7d569c8d8504a5ddbe9ac442362c65f068aeacd1f540b24ca1ec84b7c27359e  /home/learner/scripts/deploy.sh

Exit status: 0. The command completed successfully in the training fixture.

$ nginx -t

nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful

Exit status: 0. The command completed successfully in the training fixture.

Try a variation

Repeat this workflow in the sandbox with a different scratch filename. Keep the system fixtures unchanged and compare the observed output with your expectation before moving on.

Explain it

In “Incident bad deploy”, which interpretation is safe?A checksum detects changes only relative to a trusted expected digest.A command appearing in history proves it completed successfully.A successful first check guarantees that every dependent service is healthy.

Apply it elsewhere

Before adapting the sha256sum workflow from “Incident bad deploy” to another server, what should you do?Paste the training paths unchanged into production.Skip output inspection whenever the command is familiar.Confirm the current directory, target identity, permissions, and the installed command behavior first.

Keep the momentum.

Complete the lab, then explain and apply the pattern.

Next: Incident unknown listener Try an incident drill

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