The CoreMedia Ingest Service is located behind a gateway which limits the maximum response time of an API call to 30 seconds by default. If this limit is exceeded, clients will receive a Service Unavailable (503) response from the gateway even though the request may successfully finish on the service side.
There are two types of API calls that are prone to request timeouts, running synchronous bulk operations (see Bulk Operations and using UrlBlobProperty models for very large (in the range of some hundred megabytes) binary objects (see [binary-objects]).