This is a Beta release of the Sockets API. This API is not covered by any SLA
or deprecation policy and may be subject to backward-incompatible changes.
Important: Applications in the Java 8 runtime default to using native Java sockets with no restrictions: Google recommends that you keep this default. This includes the ability to use the NIO classes and methods, unlike Java 7 runtime apps, which are subject to the sockets limitations described on this page.
Sockets are only available for paid apps, and traffic from sockets is billed as outgoing bandwidth. Sockets are also limited by daily and per minute (burst) quotas.
The Java 7 runtime does not support
java.nio classes, or the ability to call get or set options against sockets.
Using these features will raise
Not Implemented exceptions. These restrictions\
are lifted by default when using the Java 8 runtime.
The supported options for Java 7 runtime apps are:
Limitations and restrictions (Java 7 runtime only)
Although App Engine supports sockets, there are certain limitations and behaviors you need to be aware of when using sockets in the Java 7 runtime:
- Sockets are available only for paid apps.
- You cannot create a listen socket; you can only create outbound sockets.
- FTP is not supported.
java.net.URLis still configured to use the URL Fetch API in the Java 7 runtime. To get around this limitation, you can run your app in the Java 8 runtime, where
java.net.HttpURLConnectionuse Java native sockets by default.
- InetAddress.isReachable is a no-op.
- Most classes in
- 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 (except those whitelisted below), are blocked:
- Google Public DNS:
- Gmail SMTPS:
smtp.gmail.comport 465 and 587
- Gmail POP3S:
- Gmail IMAPS:
- Google Public DNS:
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 2 minutes of inactivity; any socket operation keeps the socket alive for a further 2 minutes.
- You cannot
Selectbetween multiple available sockets because that requires
java.nio.SocketChannelwhich is not currently supported.)
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.
App Engine sample using sockets (Java 7 runtime only)
For a sample using sockets, see the socket demo app in the Google Cloud Platform GitHub.