TOS allows you to tag objects for classified management. You can use tags to filter objects when configuring lifecycle rules or replicating objects. This topic provides information about object tags and explains how to use them to manage objects.

Constraints and limitations

Each tag is a key-value pair. The following are the tag restrictions:

Category	Description
Billing	The object tagging feature is currently offered free of charge. We will notify you of the charging schedule and billing standards. Please stay tuned.
Number of tags	Each object can have up to ten tags, and the key cannot be duplicated for the same object.
Key-value pair	The key length cannot exceed 128 characters. The value length cannot exceed 256 characters. Both the key and the value are case-sensitive. Valid characters include uppercase and lowercase letters, numbers, spaces, and special symbols (_ .: / = + -).
Others	If you want to set object tags via an HTTP header and the tags contain special characters, both the key and the value must be URL-encoded. Modifying an object's tags does not update its last modified time. Object tags are not replicated during cross-region replication or same-region replication.

Use cases

Configuring lifecycle rules with object tags

You can use tags to filter objects when configuring lifecycle rules. For example, if you use a lifecycle rule to delete objects in batches or change their storage type, only objects with the specified tags will be affected. For instructions, see Configuring lifecycle rules based on last modified time and Configuring lifecycle rules based on last access time.

Example: The latest version of any object tagged with data:image will be deleted if it has not been modified for 120 days.

{
"Rules": [{
"ID": "id",
"Tags": {
"Key": "data",
"Value": "image"
},
"Status": "Enabled",
"Expiration": {
"Days": "120"
}
}]
}

Replicating objects with tags

You can use tags to filter objects when configuring cross-region or same-region replication rules. In other words, the rule will only replicate objects with those tags. For instructions, see Cross-region replication overview and Same-region replication overview.

Example: The latest and historical versions of objects tagged with data:image in the source bucket will be replicated to the bucket "Target Bucket Name".

{
"Role": "ServiceRoleforReplicationAccessTOS",
"Rules": [{
"ID": "1",
"Status": "Enabled",
"Tags": {
"Key": "data",
"Value": "image"
},
"Destination": {
"Bucket": "Target Bucket Name",
"Location": "cn-beijing",
"StorageClass": "STANDARD"
},
"HistoricalObjectReplication": "Enabled",
"AccessControlTranslation": {
"Owner": "BucketOwnerEntrusted"
}
}]
}

Permissions required

Before setting object tags, make sure that you have the necessary permissions for object tagging. Only the bucket creator and users with read-write permissions can read or write tags. You can grant these permissions to users through bucket policies. For more information, see Bucket policies. The relevant operations are described as follows: