Docker logging drivers - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to run a Docker container with the default logging driver.

Docker

docker run --log-driver=[1] nginx

Drag options to blanks, or click blank then click option'

Ajson-file

Bsyslog

Cnone

Djournald

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'none' disables logging, which is not default.

Choosing 'syslog' or 'journald' requires extra setup.

The default Docker logging driver is json-file, which stores logs as JSON on the local disk.

2fill in blank

medium

Complete the command to run a Docker container using the syslog logging driver.

Docker

docker run --log-driver=[1] alpine echo hello

Drag options to blanks, or click blank then click option'

Ajson-file

Bfluentd

Cnone

Dsyslog

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'json-file' will keep logs local, not send to syslog.

Choosing 'none' disables logging.

The syslog logging driver sends container logs to the syslog daemon on the host.

3fill in blank

hard

Fix the error in the command to disable logging for a container.

Docker

docker run --log-driver=[1] busybox echo test

Drag options to blanks, or click blank then click option'

Asyslog

Bjson-file

Cnone

Djournald

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'json-file' or 'syslog' will still produce logs.

Choosing 'journald' sends logs to systemd journal, not disables.

Setting the logging driver to none disables logging for the container.

4fill in blank

hard

Fill both blanks to configure a container to use the fluentd logging driver with a custom address.

Docker

docker run --log-driver=[1] --log-opt [2]=192.168.1.100:24224 alpine echo hi

Drag options to blanks, or click blank then click option'

Afluentd

Bsyslog-address

Cfluentd-address

Djson-file

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'syslog-address' option with fluentd driver is incorrect.

Choosing 'json-file' driver does not support fluentd options.

The fluentd logging driver sends logs to a Fluentd collector. The option fluentd-address sets the collector's address.

5fill in blank

hard

Fill all three blanks to create a Docker daemon configuration file snippet that sets the default logging driver to json-file with max size 10m and max files 3.

Docker

{
  "log-driver": "[1]",
  "log-opts": {
    "max-size": "[2]",
    "max-file": "[3]"
  }
}

Drag options to blanks, or click blank then click option'

Ajson-file

Bjournald

C10m

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'journald' instead of 'json-file' changes the logging system.

Setting max-size or max-file to wrong values causes config errors.

This JSON config sets the Docker daemon to use json-file as the default logging driver, limits log file size to 10m, and keeps 3 rotated files.

Practice

1. What is the default Docker logging driver used if none is specified?

easy

A. none

B. syslog

C. journald

D. json-file

Solution

1. Step 1: Understand Docker default logging behavior

   Docker uses a default logging driver to store container logs unless changed.

2. Step 2: Identify the default driver

   The default driver is json-file, which stores logs as JSON files on the host.

3. Final Answer:

   json-file -> Option D

4. Quick Check:

   Default logging driver = json-file [OK]

Hint: Default is json-file unless changed in daemon config [OK]

Common Mistakes:

• Choosing syslog as default
• Thinking none disables logging by default
• Confusing journald with default

2. Which of the following is the correct syntax to set the logging driver to syslog when running a container?

easy

A. docker run --log-driver=syslog myimage

B. docker run --logging=syslog myimage

C. docker run --logdriver=syslog myimage

D. docker run --log syslog myimage

Solution

1. Step 1: Recall Docker run command options for logging

   The correct flag to specify logging driver is --log-driver.

2. Step 2: Match the correct syntax

   docker run --log-driver=syslog myimage uses --log-driver=syslog, which is the correct syntax.

3. Final Answer:

   docker run --log-driver=syslog myimage -> Option A

4. Quick Check:

   Use --log-driver to set logging driver [OK]

Hint: Use --log-driver=driver_name to set logging driver [OK]

Common Mistakes:

• Using --logging instead of --log-driver
• Missing the dash in --log-driver
• Using --log instead of --log-driver

3. Given the command:
docker run --log-driver=json-file --log-opt max-size=10m --log-opt max-file=3 alpine echo hello
What will happen when the container logs exceed 30 MB?

medium

A. Logs will grow indefinitely without rotation

B. Logs will be deleted immediately after 30 MB

C. Logs will be rotated and only the latest 3 files of 10 MB each are kept

D. Container will stop running when logs exceed 30 MB

Solution

1. Step 1: Understand log options max-size and max-file

   max-size=10m means each log file max is 10 MB; max-file=3 means keep 3 rotated files.

2. Step 2: Calculate total log size before rotation

   3 files x 10 MB each = 30 MB total before old logs are deleted.

3. Final Answer:

   Logs will be rotated and only the latest 3 files of 10 MB each are kept -> Option C

4. Quick Check:

   max-size and max-file control log rotation [OK]

Hint: max-size x max-file = total log size before rotation [OK]

Common Mistakes:

• Thinking logs delete immediately at 30 MB
• Assuming container stops on log size limit
• Ignoring max-file setting

4. You run a container with:
docker run --log-driver=none nginx
But you still see logs when running docker logs. What is the likely cause?

medium

A. The --log-driver=none flag is invalid and ignored

B. The container was started before the logging driver was set to none

C. Docker logs command shows logs from the host system

D. The container image nginx forces logging regardless of driver

Solution

1. Step 1: Understand effect of --log-driver=none

   This disables logging for the container started with this flag.

2. Step 2: Consider container start timing

   If the container was started before setting the flag, old logs remain accessible.

3. Final Answer:

   The container was started before the logging driver was set to none -> Option B

4. Quick Check:

   Logging driver applies only at container start [OK]

Hint: Logging driver must be set when container starts [OK]

Common Mistakes:

• Assuming --log-driver=none is invalid
• Thinking docker logs shows host logs
• Believing image controls logging driver

5. You want to configure Docker daemon to use the journald logging driver by default and limit log file size to 5 MB with 2 rotated files. Which daemon.json configuration is correct?

hard

A. {
"log-driver": "journald",
"log-opts": {
"max-size": "5m",
"max-file": "2"
}
}

B. {
"logging-driver": "journald",
"logging-opts": {
"max-size": "5m",
"max-file": "2"
}
}

C. {
"log-driver": "journald",
"log-opts": {
"max-size": 5,
"max-file": 2
}
}

D. {
"log-driver": "journald",
"log-opts": {
"max-size": "5MB",
"max-file": "2"
}
}

Solution

1. Step 1: Identify correct keys in daemon.json

   The keys are "log-driver" and "log-opts" (not "logging-driver" or "logging-opts").

2. Step 2: Check value formats for options

   max-size must be a string with units like "5m" (not number or "5MB" which is invalid).

3. Final Answer:

   { "log-driver": "journald", "log-opts": { "max-size": "5m", "max-file": "2" } } -> Option A

4. Quick Check:

   Use "log-driver" and string values with units [OK]

Hint: Use "log-driver" and string sizes like "5m" in daemon.json [OK]

Common Mistakes:

• Using wrong keys like logging-driver
• Using numeric values without units
• Using invalid units like MB instead of m