Content filtering in Amazon EventBridge event patterns

Amazon EventBridge supports declarative content filtering using event patterns. With content filtering, you can write complex event patterns that only match events under very specific conditions. For example, you can create an event pattern that matches an event when a field of the event is within a specific numeric range, if the event comes from a specific IP address, or only if a specific field doesn't exist in the event JSON.

Important

In EventBridge, it is possible to create rules that lead to infinite loops, where a rule is fired repeatedly. For example, a rule might detect that ACLs have changed on an S3 bucket, and trigger software to change them to the desired state. If the rule is not written carefully, the subsequent change to the ACLs fires the rule again, creating an infinite loop.

To prevent this, write the rules so that the triggered actions do not re-fire the same rule. For example, your rule could fire only if ACLs are found to be in a bad state, instead of after any change.

An infinite loop can quickly cause higher than expected charges. We recommend that you use budgeting, which alerts you when charges exceed your specified limit. For more information, see Managing Your Costs with Budgets.

Prefix matching

You can match an event depending on the prefix of a value in the event source. You can use prefix matching for string values.

For example, the following event pattern would match any event where the "time" field started with "2017-10-02" such as "time": "2017-10-02T18:43:48Z".

{
  "time": [ { "prefix": "2017-10-02" } ]
}

Suffix matching

You can match an event depending on the suffix of a value in the event source. You can use suffix matching for string values.

For example, the following event pattern would match any event where the "FileName" field ends with the .png file extension.

{
  "FileName": [ { "suffix": ".png" } ]
}

Anything-but matching

Anything-but matching matches anything except what's provided in the rule.

You can use anything-but matching with strings and numeric values, including lists that contain only strings, or only numbers.

The following event pattern shows anything-but matching with strings and numbers.

{
  "detail": {
    "state": [ { "anything-but": "initializing" } ]
  }
}

{
  "detail": {
    "x-limit": [ { "anything-but": 123 } ]
  }
}

The following event pattern shows anything-but matching with a list of strings.

{
  "detail": {
    "state": [ { "anything-but": [ "stopped", "overloaded" ] } ]
  }
}

The following event pattern shows anything-but matching with a list of numbers.

{
  "detail": {
    "x-limit": [ { "anything-but": [ 100, 200, 300 ] } ]
  }
}

The following event pattern shows anything-but matching that matches any event that doesn't have the prefix "init" in the "state" field.

Note

Anything-but matching only works with a single prefix, not a list.

{
  "detail": {
    "state": [ { "anything-but": { "prefix": "init" } } ]
  }
}

Numeric matching

Numeric matching works with values that are JSON numbers. It is limited to values between -5.0e9 and +5.0e9 inclusive, with 15 digits of precision, or six digits to the right of the decimal point.

The following shows numeric matching for an event pattern that only matches events that are true for all fields.

{
  "detail": {
    "c-count": [ { "numeric": [ ">", 0, "<=", 5 ] } ],
    "d-count": [ { "numeric": [ "<", 10 ] } ],
    "x-limit": [ { "numeric": [ "=", 3.018e2 ] } ]
  }
}

IP address matching

You can use IP address matching for IPv4 and IPv6 addresses. The following event pattern shows IP address matching to IP addresses that start with 10.0.0 and end with a number between 0 and 255.

{
  "detail": {
    "sourceIPAddress": [ { "cidr": "10.0.0.0/24" } ]
  }
}

Exists matching

Exists matching works on the presence or absence of a field in the JSON of the event.

Exists matching only works on leaf nodes. It does not work on intermediate nodes.

The following event pattern matches any event that has a detail.state field.

{
  "detail": {
    "state": [ { "exists": true  } ]
  }
}

The preceding event pattern matches the following event.

{
  "version": "0",
  "id": "7bf73129-1428-4cd3-a780-95db273d1602",
  "detail-type": "EC2 Instance State-change Notification",
  "source": "aws.ec2",
  "account": "123456789012",
  "time": "2015-11-11T21:29:54Z",
  "region": "us-east-1",
  "resources": ["arn:aws:ec2:us-east-1:123456789012:instance/i-abcd1111"],
  "detail": {
    "instance-id": "i-abcd1111",
    "state": "pending"
  }
}

The preceding event pattern does NOT match the following event because it doesn't have a detail.state field.

{
  "detail-type": [ "EC2 Instance State-change Notification" ],
  "resources": [ "arn:aws:ec2:us-east-1:123456789012:instance/i-02ebd4584a2ebd341" ],
  "detail": {
    "c-count" : {
       "c1" : 100
    }
  }
}

Equals-ignore-case matching

Equals-ignore-case matching works on string values regardless of case.

The following event pattern matches any event that has a detail-type field that matches the specified string, regardless of case.

{
  "detail-type": [ { "equals-ignore-case": "ec2 instance state-change notification" } ]
}

The preceding event pattern matches the following event.

{
  "detail-type": [ "EC2 Instance State-change Notification" ],
  "resources": [ "arn:aws:ec2:us-east-1:123456789012:instance/i-02ebd4584a2ebd341" ],
  "detail": {
    "c-count" : {
       "c1" : 100
    }
  }
}

Complex example with multiple matching

You can combine multiple matching rules into a more complex event pattern. For example, the following event pattern combines anything-but and numeric.

{
  "time": [ { "prefix": "2017-10-02" } ],
  "detail": {
    "state": [ { "anything-but": "initializing" } ],
    "c-count": [ { "numeric": [ ">", 0, "<=", 5 ] } ],
    "d-count": [ { "numeric": [ "<", 10 ] } ],
    "x-limit": [ { "anything-but": [ 100, 200, 300 ] } ]
  }
}

Note

When building event patterns, if you include a key more than once the last reference will be the one used to evaluate events. For example, for the following pattern:

{
  "detail": {
    "location": [ { "prefix": "us-" } ],
    "location": [ { "anything-but": "us-east" } ]
  }
}

only { "anything-but": "us-east" } will be taken into account when evaluating the location.

Complex example with $or matching

You can also create complex event patterns that check to see if any field values match, across multiple fields. Use $or to create an event pattern that matches if any of the values for multiple fields are matched.

Note that you can include other filter types, such as numeric matching and arrays, in your pattern matching for individual fields in your $or construct.

The following event pattern matches if any of the following conditions are met:

• The c-count field is greater than 0 or less than or equal to 5.

• The d-count field is less than 10.

• The x-limit field equals 3.018e2.

{
  "detail": {
    "$or": [
      { "c-count": [ { "numeric": [ ">", 0, "<=", 5 ] } ] },
      { "d-count": [ { "numeric": [ "<", 10 ] } ] },
      { "x-limit": [ { "numeric": [ "=", 3.018e2 ] } ] }
    ]
  }
}

Note

APIs that accept an event pattern (such as PutRule, CreateArchive, UpdateArchive, and TestEventPattern) will throw an InvalidEventPatternException if the use of $or results in over 1000 rule combinations.

To determine the number of rule combinations in an event pattern, multiply the total number of arguments from each $or array in the event pattern. For example, the above pattern contains a single $or array with three arguments, so the total number of rule combinations is also three. If you added another $or array with two arguments, the total rule combinations would then be six.