503 Service Unavailable
503 Service Unavailable is a status that a server can send when it is
overloaded, or otherwise incapable of handling a request. Maybe the server is
just booting up, or perhaps the application is partially down.
When this status is returned, a server can optionally include a
header to tell a client when to try the request again.
HTTP/1.1 503 Service Unavailable Content-Type text/plain Retry-After: 1800 System overload! Give us some time to increase capacity.
- RFC7231, Section 6.6.4 - 503 Service Unavailable