Common container startup failures in Docker - Step-by-Step Execution

Process Flow - Common container startup failures

Start container

↓

Check container status

↓

Is container running?

No→Check logs

↓

Identify error

↓

Container ready

↓

Fix issue

↓

Restart container

↓

Check container status

This flow shows how a container starts, checks if it runs, and if not, logs are checked to find and fix errors before restarting.

Execution Sample

Docker

docker run myapp
# Container fails to start
docker logs <container_id>
# Shows error: missing config
# Fix config
# Restart container

This sequence runs a container, checks logs on failure, fixes the problem, and restarts the container.

Process Table

Step	Action	Result	Next Step
1	Run container with 'docker run myapp'	Container starts but exits immediately	Check container status
2	Check container status	Container is not running	Check logs
3	Run 'docker logs <container_id>'	Error: missing config file	Identify error
4	Fix missing config file	Config file added	Restart container
5	Restart container	Container starts successfully and runs	Container ready
6	Check container status	Container is running	Process complete

💡 Container runs successfully after fixing config and restarting

Status Tracker

Variable	Start	After Step 1	After Step 3	After Step 4	After Step 5	Final
container_status	not started	exited	exited	exited	running	running
error_message	none	none	missing config file	none	none	none
config_file	missing	missing	missing	added	added	added

Key Moments - 3 Insights

Why does the container exit immediately after starting?

The container exits because it lacks a required config file, as shown in step 3's logs in the execution_table.

How do logs help in fixing startup failures?

Logs reveal the exact error causing failure, like the missing config file in step 3, guiding what to fix before restarting.

Why must the container be restarted after fixing the config?

Changes like adding a config file only take effect when the container restarts, shown by the status change from 'exited' to 'running' after step 5.

Visual Quiz - 3 Questions

Look at the execution_table, what is the container_status after step 1?

A exited

B running

C not started

D paused

💡 Hint

Check the 'container_status' variable in variable_tracker after Step 1

At which step does the error 'missing config file' appear?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the 'error_message' variable in variable_tracker and the 'Result' column in execution_table

If the config file was not fixed at step 4, what would happen at step 5?

A Container would start successfully

B Container would pause

C Container would still exit immediately

D Container would crash the host

💡 Hint

Refer to the 'container_status' and 'config_file' variables in variable_tracker

Concept Snapshot

Common container startup failures:
- Run container with 'docker run'
- If container exits, check status with 'docker ps -a'
- Use 'docker logs <id>' to see errors
- Fix issues like missing config files
- Restart container to apply fixes
- Repeat until container runs successfully

Full Transcript

This visual execution shows how a container can fail to start due to common issues like missing configuration files. First, the container is started but exits immediately. Checking the container status confirms it is not running. Logs reveal the error message about the missing config file. After adding the config file, the container is restarted. This time it starts and runs successfully. Variables like container status, error messages, and config file presence are tracked step-by-step to understand the process. Key moments include understanding why the container exits, how logs help identify problems, and why restarting is necessary after fixes.