Docker logging drivers - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of Docker container logs with json-file driver

You run a Docker container with the default logging driver (json-file). What will be the output of docker logs mycontainer if the container prints Hello World once and then exits?

Docker

docker run --name mycontainer alpine echo Hello World
docker logs mycontainer

A

Error: No logs available

B

Hello World

C

Container started
Hello World
Container exited

D Hello World (with JSON metadata lines)

💡 Hint

The default json-file driver stores logs in JSON but docker logs shows only the message content.

The json-file driver stores logs as JSON internally, but the docker logs command outputs only the container's stdout/stderr content, so you see just 'Hello World'.

🧠 Conceptual

intermediate

Understanding Docker logging driver options

Which Docker logging driver is designed to send container logs directly to the systemd journal?

A journald

B fluentd

C syslog

D json-file

💡 Hint

Systemd journal is a logging system used by many Linux distributions.

The 'journald' logging driver sends container logs to the systemd journal, integrating with the system's native logging.

❓ Troubleshoot

advanced

Diagnosing Docker logging driver misconfiguration

You configured a Docker container to use the 'fluentd' logging driver but see no logs in your Fluentd server. Which of the following is the most likely cause?

A The container logs are too large to send

B The container is using the default json-file driver instead

C The Fluentd server is not reachable at the configured address

D Docker does not support the fluentd driver

💡 Hint

Check network connectivity and configuration between Docker and Fluentd.

If the Fluentd server is unreachable, Docker cannot send logs, causing no logs to appear. The fluentd driver is supported and must be reachable.

🔀 Workflow

advanced

Configuring Docker container with syslog logging driver

You want to run a Docker container that sends logs to a remote syslog server at 192.168.1.100 on port 514 using UDP. Which command correctly sets this up?

A docker run --log-driver=json-file --log-opt syslog-address=udp://192.168.1.100:514 alpine echo test

B docker run --log-driver=fluentd --log-opt address=udp://192.168.1.100:514 alpine echo test

C docker run --log-driver=syslog --log-opt syslog-address=tcp://192.168.1.100:514 alpine echo test

D docker run --log-driver=syslog --log-opt syslog-address=udp://192.168.1.100:514 alpine echo test

💡 Hint

The syslog logging driver uses the option 'syslog-address' with protocol and IP.

Option D correctly uses the syslog driver with UDP protocol and the correct option name. Option D uses TCP instead of UDP. Option D uses the wrong driver. Option D uses json-file driver which ignores syslog options.

✅ Best Practice

expert

Choosing the best logging driver for high-volume production containers

For a high-volume production environment where you want centralized log management with minimal performance impact on containers, which Docker logging driver is generally recommended?

A fluentd

B json-file

C none

D local

💡 Hint

Centralized log management often uses external log collectors.

The fluentd driver sends logs to an external collector, reducing local disk usage and enabling centralized management. json-file stores logs locally which can impact disk and performance. none disables logging. local is for local optimized storage but not centralized.