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How to manage Amazon S3 Object Metadata (Key/Value pairs)?

Object key: The name assign to an object and is used to retrieve the Object.

Each file and folder stored on Amazon S3 has a set of key value pairs called metadata or headers . Metadata provides some basic and important details about the file.

There are two types of metadata for files on S3 :

Protocol defined information is attached automatically as defined in specifications of that protocol. This information helps the files to be recognized under that protocol domain.

  1. System metadata :
    System metadata is used and processed by Amazon S3. This information helps the receiver to understand the file details without the need to open it. We can understand this Metadata by the example of "Content-type" which is system defined.
  2. User metadata :
    User metadata or custom header is specified by you. Amazon S3 simply stores and passes it back to you when you ask for it.
    When Metadata is retrieved through REST API, Amazon S3 combines headers that have the same name (ignoring case) into a comma-delimited list. If some Metadata contains unprintable characters, it is not returned. Instead, the "x-amz-missing-meta" header is returned with a value of the number of unprintable Metadata entries.

You can also change the Storage-Class for an object while updating metadata.

Storage Types of S3 Objects:

  1. STANDARD
    It is a storage option that replicates objects. It is designed to sustain the concurrent loss of data in two facilities. By default, S3 Object has STANDARD Storage class type.
  2. REDUCED-REDUNDACY
    It is a storage option that allows users to reduce costs by storing non-critical, reproducible data at lower levels of redundancy.
  3. GLACIER
    It is a storage option for data that are not frequently used or "cold data". It is an extremely low-cost storage service. It provides a secure storage for archiving data and taking back-up. It also allows you to store data cost effectively for a long time, for months, years, and even decades.

Note: Metadata size is limited to 2k bytes for the total length of all values and keys.

Bucket Explorer has an option for you to upload file(s) at Amazon S3 with Custom Header. Every uploading file has its own system Metadata , and using this feature, you can customize Metadata detail for the uploading file and folder. You can even Set/Edit the system Metadata for the file .

Here are the steps to upload files on Amazon S3 with custom header
  1. Run Bucket Explorer.
  2. Select a Bucket in which you want to upload a file .
  3. Select the file(s) that you want to upload with custom header from the left panel tree and right click on the selected file(s).
  4. Now select " Upload with Custom Headers " option.
  5. A dialog box entitled "Upload with custom header" will appear. Click on "Add" button and it will ask for Key and value.
  6. Enter data for key and value. Key name does not contain any space and other constraints that are followed by Metadata.
  7. Click on OK button.
  1. Uploading process will start in queue. After completion of queue, you can see the statistics panel for the status of the upload process .
  2. The file(s) will then be uploaded.
  3. Refresh object listing so that you can see the uploaded file(s).
  4. Right click on the uploaded file and choose " Properties " option.
  5. You will find the Metadata added in the properties of the file.
  6. Only files within a folder will show Metadata in their properties and not the folder even if you upload the folder with custom header.
    Note : Repeat this step with a folder + one file (i.e. select a folder and a file on the same level on local system) and then check it again and check the properties on all uploaded files. The Metadata values will be saved for all the files that have been uploaded including files under a folder and the selected single file.
  7. If you upload the same file with different custom header, you will be asked to Overwrite or Skip the file.
  8. After completing the uploading process, the new Metadata will not be saved with the identical file's properties.
  9. Now change the content of the file at local file system and upload it again with the new Metadata. You can now see the changed Metadata (Custom Header) in the properties window of the file.