Logstash Conditional Filter Cheat Sheet: The Ultimate Guide

Conditional filtering is a very important feature that helps you to process data based on different conditions.

This tutorial, will show you how to use conditional filtering in Logstash with the if/else statement.

1. Conditional Filtering in Logstash

To filter data conditionally in Logstash, you can use the if/else statement: if <condition> { ... } else { ... }.

The syntax is:

if <condition> {
	# do something
} else if <condition> {
	# do something else
} else {
	# do something else
}

For example, to check if the field [event][duration] is greater than 1000, you can use the following code:

if [event][duration] > 1000 {
	# do something
} else {
	# do something else
}

2. Check if Field Exists in Logstash

To check if a field exists in Logstash, you can use if [field], which will return true if the field exists, and false if the field does not exist.

For example, to check if the field [user][name] exists, you can use the following code:

if [user][name] {
	# do something
} else {
	# do something else
}

3. Check if Field is Empty in Logstash

Similarly, to check if a field is empty in Logstash, you can use if [field] == "", which will return true if the field is empty, and false if the field is not empty.

For example, to check if the field [user][age] is missing, you can use the following code:

if [user][age] == "" {
	# do something
} else {
	# do something else
}

4. Check if Field is Null in Logstash

To check if a field is null in Logstash, you can use if [field] == nil, which will return true if the field is null, and false if the field is not null.

For example, to check if the field [user][email] is null, you can use the following code:

if [user][email] == nil {
	# do something
} else {
	# do something else
}

5. Check if Field Starts With a String in Logstash

To check if a field starts with a string in Logstash, you can use if [field] =~ /^<string>/, which will return true if the field starts with the string, and false if the field does not start with the string.

For example, to check if the field [user][name] starts with the string Minh, you can use the following code:

if [user][name] =~ /^Minh/ {
	# do something
} else {
	# do something else
}

Conclusion

In this tutorial, we learned how to use conditional filtering in Logstash with the if/else statement.

There are some common cases that need the help of conditional filtering, such as:

1. Check if a field exists in Logstash: if [field]
2. Check if a field is empty in Logstash: if [field] == ""
3. Check if a field is null in Logstash: if [field] == nil
4. Check if a field starts with a string in Logstash: if [field] =~ /^<string>/

I hope this helps and see you in the next tutorial!