Note: Go 1.11 has reached end of support on January 30, 2024. Your existing Go 1.11 applications will continue to run and receive traffic. However, App Engine might block re-deployment of applications that use runtimes after their end of support date. We recommend that you migrate to the latest supported version of Go.

Sockets API for legacy bundled services

Traffic from sockets is billed as outgoing bandwidth. App Engine supports outbound sockets through the appengine/socket package.

Libraries that can accept a net.Conn should work without modification.

Limitations and restrictions

Socket support in App Engine has the following limitations:

You cannot create a listen socket; you can only create outbound sockets.
FTP is not supported.
You can only use TCP or UDP; arbitrary protocols are not allowed.
You cannot bind to specific IP addresses or ports.
Port 25 (SMTP) is blocked; you can still use authenticated SMTP on the submission port 587.
Private, broadcast, multicast, and Google IP ranges are blocked, except those listed below:
- Google Public DNS: 8.8.8.8, 8.8.4.4, 2001:4860:4860::8888, 2001:4860:4860::8844 port 53
- Gmail SMTPS: smtp.gmail.com port 465 and 587
- Gmail POP3S: pop.gmail.com port 995
- Gmail IMAPS: imap.gmail.com port 993
Note: Google Compute Engine IP addresses are not considered to be in Google IP ranges. You can use sockets to connect App Engine apps to Compute Engine instances.
Socket descriptors are associated with the App Engine app that created them and are non-transferable (cannot be used by other apps).
Sockets may be reclaimed after 10 minutes of inactivity; any socket operation keeps the socket alive for a further 10 minutes.
Using sockets with the development server

You can run and test code using sockets on the development server, without using any special command line parameters.