<p>Specifies a unique, case-sensitive identifier that you provide to ensure the idempotency of the request. This lets you safely retry the request without accidentally performing the same operation a second time. Passing the same value to a later call to an operation requires that you also pass the same value for all other parameters. We recommend that you use a <a href="https://wikipedia.org/wiki/Universally_unique_identifier">UUID type of value</a>.</p> <p>If you don't provide this value, then Amazon Web Services generates a random one for you.</p> <p>If you retry the operation with the same <code>ClientToken</code>, but with different parameters, the retry fails with an <code>IdempotentParameterMismatch</code> error.</p>