Log groups and log streams in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Log Group Retention

You create a CloudWatch Log Group with a retention period of 7 days. What happens to the log data after 7 days?

A The log data is moved to a new log stream after 7 days.

B The log data is archived indefinitely after 7 days.

C The log data is automatically deleted after 7 days.

D The log data remains until you manually delete the log group.

💡 Hint

Think about what retention means for data lifecycle.

Retention period defines how long logs are kept. After that, logs are deleted automatically.

❓ Architecture

intermediate

Log Stream Creation Behavior

Which statement best describes when a new log stream is created in a CloudWatch Log Group?

A A new log stream is created automatically for each unique source sending logs.

B You must manually create all log streams before sending logs.

C Log streams are created only when you enable log retention.

D Log streams are created only when you delete the log group.

💡 Hint

Consider how logs from different sources are organized.

CloudWatch creates a new log stream automatically for each unique source or resource sending logs to a log group.

❓ service_behavior

advanced

Log Stream Sequence Token Usage

You are sending log events to a CloudWatch Log Stream using the AWS SDK. What happens if you send a batch of log events with an incorrect sequence token?

A The log events overwrite previous events in the stream.

B The log events are accepted but stored out of order.

C The log stream is deleted automatically.

D The API call fails with an InvalidSequenceTokenException error.

💡 Hint

Think about how CloudWatch ensures log event order.

CloudWatch requires the correct sequence token to maintain order. An incorrect token causes an error.

❓ security

advanced

IAM Permissions for Log Group Access

Which IAM permission is required to allow a user to create a new log stream in an existing CloudWatch Log Group?

A logs:CreateLogStream

B logs:CreateLogGroup

C logs:PutLogEvents

D logs:DeleteLogStream

💡 Hint

Focus on the permission that allows creating streams, not sending logs.

The logs:CreateLogStream permission allows creating new log streams within a log group.

✅ Best Practice

expert

Optimizing Log Group Design for Multiple Applications

You manage logs for multiple applications in your AWS account. Which approach is best to organize CloudWatch Log Groups and Log Streams for clear separation and easy management?

A Create one log stream per application and multiple log groups per application instance.

B Create one log group per application and multiple log streams per application instance.

C Create one log group for all applications and one log stream per application.

D Create one log group and one log stream for all applications combined.

💡 Hint

Think about how to separate logs logically and manage retention easily.

Creating one log group per application allows setting retention and access controls per app. Multiple log streams per instance keep logs organized.

Practice

1. What is the main purpose of a log group in AWS CloudWatch Logs?

easy

A. To organize multiple log streams into a single container

B. To store individual log events directly

C. To control user access to AWS services

D. To monitor AWS billing and cost usage

Solution

1. Step 1: Understand log group role

   A log group acts as a container for multiple log streams, grouping logs by application or resource.

2. Step 2: Differentiate from other options

   Log events are stored in log streams, not directly in log groups. Access control and billing are unrelated.

3. Final Answer:

   To organize multiple log streams into a single container -> Option A

4. Quick Check:

   Log group = container for log streams [OK]

Hint: Log groups hold streams, streams hold logs [OK]

Common Mistakes:

• Confusing log groups with log streams
• Thinking logs are stored directly in log groups
• Mixing log groups with access control or billing

2. Which of the following is the correct way to create a log stream named appStream inside a log group appGroup using AWS CLI?

easy

A. aws logs create-log-group --log-stream-name appStream --log-group-name appGroup

B. aws logs create-log-stream --name appStream --group appGroup

C. aws logs create-log-stream appGroup appStream

D. aws logs create-log-stream --log-group-name appGroup --log-stream-name appStream

Solution

1. Step 1: Identify correct AWS CLI command syntax

   The command to create a log stream is aws logs create-log-stream with parameters --log-group-name and --log-stream-name.

2. Step 2: Verify aws logs create-log-stream --log-group-name appGroup --log-stream-name appStream matches syntax

   aws logs create-log-stream --log-group-name appGroup --log-stream-name appStream correctly uses the command and parameters in the right order and names.

3. Final Answer:

   aws logs create-log-stream --log-group-name appGroup --log-stream-name appStream -> Option D

4. Quick Check:

   Correct CLI syntax = aws logs create-log-stream --log-group-name appGroup --log-stream-name appStream [OK]

Hint: Remember: create-log-stream needs both group and stream names [OK]

Common Mistakes:

• Using create-log-group instead of create-log-stream
• Swapping parameter names
• Omitting required flags

3. Given the following AWS CLI commands executed in order:

aws logs create-log-group --log-group-name myAppLogs
aws logs create-log-stream --log-group-name myAppLogs --log-stream-name stream1
aws logs put-log-events --log-group-name myAppLogs --log-stream-name stream1 --log-events '[{"timestamp":1609459200000,"message":"Start"}]'
aws logs describe-log-streams --log-group-name myAppLogs

What will the describe-log-streams command output include?

medium

A. A list containing one log stream named 'stream1' with stored events

B. An empty list because no log streams exist yet

C. An error stating the log group does not exist

D. A list of all log groups in the account

Solution

1. Step 1: Trace commands creating log group and stream

   The first two commands create a log group 'myAppLogs' and a log stream 'stream1' inside it.

2. Step 2: Put log event and describe streams

   The third command adds a log event to 'stream1'. The last command lists streams in 'myAppLogs', so it will show 'stream1' with events.

3. Final Answer:

   A list containing one log stream named 'stream1' with stored events -> Option A

4. Quick Check:

   Created stream appears in describe output [OK]

Hint: Create group and stream before putting logs [OK]

Common Mistakes:

• Expecting empty list before adding streams
• Confusing log groups with streams in output
• Assuming describe lists groups, not streams

4. You run this AWS CLI command:

aws logs put-log-events --log-group-name myGroup --log-stream-name myStream --log-events '[{"timestamp":1609459200000,"message":"Hello"}]'

But you get an error saying the log stream does not exist. What is the most likely fix?

medium

A. Remove the timestamp from the log event

B. Change the log group name to an existing group

C. Create the log stream 'myStream' inside 'myGroup' before putting events

D. Use the create-log-group command instead

Solution

1. Step 1: Understand error cause

   The error indicates the log stream 'myStream' does not exist in 'myGroup'. You must create the stream before sending logs.

2. Step 2: Identify correct fix

   Creating the log stream with aws logs create-log-stream resolves the error. Changing group or removing timestamp won't help.

3. Final Answer:

   Create the log stream 'myStream' inside 'myGroup' before putting events -> Option C

4. Quick Check:

   Log stream must exist before putting logs [OK]

Hint: Create log stream first to avoid put-log-events error [OK]

Common Mistakes:

• Trying to put logs before stream creation
• Ignoring error details about missing stream
• Confusing log group creation with stream creation

5. You want to organize logs from multiple microservices in AWS CloudWatch. Each microservice should have its own log stream, but all streams must be grouped for easy management and retention. Which setup is best?

hard

A. Store logs outside CloudWatch to avoid managing groups and streams

B. Create one log group for all microservices, and create separate log streams for each microservice inside it

C. Create one log group per microservice and put all logs in a single stream inside each group

D. Create one log stream per microservice without using log groups

Solution

1. Step 1: Understand grouping and streaming roles

   Log groups organize logs for management and retention. Log streams separate logs by source within groups.

2. Step 2: Choose best structure for microservices

   Using one log group for all microservices and separate streams per microservice allows easy management and searching.

3. Step 3: Evaluate other options

   Create one log stream per microservice without using log groups lacks grouping, C creates many groups complicating retention, A ignores CloudWatch benefits.

4. Final Answer:

   Create one log group for all microservices, and create separate log streams for each microservice inside it -> Option B

5. Quick Check:

   Group = container; streams = sources [OK]

Hint: Group logs by app, stream by source inside group [OK]

Common Mistakes:

• Skipping log groups and using only streams
• Creating too many log groups unnecessarily
• Ignoring CloudWatch log management features