forking child process in server causes client handshake failures

[AK]

I am trying to make grpc server a daemon by forking a child and making it exit. But after that the client handshake starts to fail.

E0307 01:15:58.221786152   27094 handshake.c:128]            Security handshake failed: {"created":"@1488878158.221756436","description":"Handshake read failed","file":"src/core/lib/security/transport/handshake.c","file_line":237,"referenced_errors":[{"created":"@1488878158.221740996","description":"FD shutdown","file":"src/core/lib/iomgr/ev_epoll_linux.c","file_line":948}]}

This happens if fork() is called after the call to BuildAndStart(). If the same fork is done before BuildAndStart() everything works fine.

[Nicolas Noble]

Does the forked child do any gRPC call at all ? Also, which language ?

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[AK]

The forked child simply exits leaving the parent as daemon. I am doing it in C++ on Ubuntu.

On Tuesday, March 7, 2017 at 12:07:40 PM UTC-8, Nicolas Noble wrote:

Does the forked child do any gRPC call at all ? Also, which language ?

On Tue, Mar 7, 2017 at 9:40 AM, AK <anand.s...@gmail.com> wrote:

I am trying to make grpc server a daemon by forking a child and making it exit. But after that the client handshake starts to fail.

E0307 01:15:58.221786152   27094 handshake.c:128]            Security handshake failed: {"created":"@1488878158.221756436","description":"Handshake read failed","file":"src/core/lib/security/transport/handshake.c","file_line":237,"referenced_errors":[{"created":"@1488878158.221740996","description":"FD shutdown","file":"src/core/lib/iomgr/ev_epoll_linux.c","file_line":948}]}

This happens if fork() is called after the call to BuildAndStart(). If the same fork is done before BuildAndStart() everything works fine.

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[Ken Payson]

Are you calling any destructors in the forked process before exit?  Destroying the server will call shutdown() on the underlying sockets, which will cause problems for the parent process.

Ken

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[AK]

No. The child does nothing but exit. Below is an example of what I am doing. If I move the server startup line to the end, everything works fine.

   server = std::unique_ptr<grpc::Server>(builder.BuildAndStart());
   int childpid = fork();
    if ( childpid )
      exit(0);

On Tuesday, March 7, 2017 at 1:03:01 PM UTC-8, Ken Payson wrote:

Are you calling any destructors in the forked process before exit?  Destroying the server will call shutdown() on the underlying sockets, which will cause problems for the parent process.

Ken

On Tue, Mar 7, 2017 at 12:19 PM, AK <anand.s...@gmail.com> wrote:

The forked child simply exits leaving the parent as daemon. I am doing it in C++ on Ubuntu.

On Tuesday, March 7, 2017 at 12:07:40 PM UTC-8, Nicolas Noble wrote:

Does the forked child do any gRPC call at all ? Also, which language ?

On Tue, Mar 7, 2017 at 9:40 AM, AK <anand.s...@gmail.com> wrote:

I am trying to make grpc server a daemon by forking a child and making it exit. But after that the client handshake starts to fail.

E0307 01:15:58.221786152   27094 handshake.c:128]            Security handshake failed: {"created":"@1488878158.221756436","description":"Handshake read failed","file":"src/core/lib/security/transport/handshake.c","file_line":237,"referenced_errors":[{"created":"@1488878158.221740996","description":"FD shutdown","file":"src/core/lib/iomgr/ev_epoll_linux.c","file_line":948}]}

This happens if fork() is called after the call to BuildAndStart(). If the same fork is done before BuildAndStart() everything works fine.

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[Ken Payson]

I'm not familiar with the interaction of unique_ptr<> and exit().

What happens if you try the following:

   grpc::Server* server_ptr = builder.BuildAndStart();

   int childpid = fork();
    if ( childpid )
      exit(0);

   server = std::unique_ptr<grpc::Server>(server_ptr);

Also, in the problem you stated, it sounded like you were forking and exiting the child immediately.  The code provided exits the parent process immediately.

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[AK]

You are right about parent exiting. Sorry, that might have caused confusion. Actually the child becomes daemon now. Does that change how secure handshake in grpc behaves ?
The builder.BuildAndStart() returns std::unqiue_ptr.
Your suggested changes seems to make no difference to process state.

[Ken Payson]

If you are forking and exiting the parent immediately, I'd suggest avoid doing any gRPC setup in the parent process.

The suggested changes were intended to avoid invoking the Server destructor.  I suspect whats happening is std::unique_ptr<> is causing the destructor to be called on exit().

That being said, I'd still recommend deferring server construction to the child process.

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