how does grpc handle DNS address changes?

[Yaz Saito]

Assume we have foo.example.com, whose value changes unpredictably.

1. Initially, the A record of foo.example.com points to, say 1.2.3.4.

2. Start a grpc client, with the server pointed at foo.example.com:10000. The client fails to

  connect since there's nothing running at 1.2.3.4:10000.

3. Start a grpc server at an IP address 1.2.3.5:10000. 

4. Update the DNS server so that foo.example.com points to 1.2.3.5.

In this situation, the grpc client never seems to discover the server at 1.2.3.5, even when I set the DNS TTL very short.

Am I diagnosing the problem correct? And if so, is there a way to work around?

--

yaz

[raut...@gmail.com]

Steps 4 and 5 should be interchanged I think.

What does host foo.example.com results in, on your computer?

Are you running your code on a Linux box or some other environment?

Thanks,

[Abhishek Parmar]

(Replying for Yaz, he is on vacation)

On Thu, Aug 18, 2016 at 4:15 PM, <raut...@gmail.com> wrote:

Steps 4 and 5 should be interchanged I think.

You mean 3 and 4 should be swapped? I don't think it matters.

 

What does host foo.example.com results in, on your computer?

Are you running your code on a Linux box or some other environment?

It is running on linux.

 

Thanks,

On Wednesday, 17 August 2016 13:49:21 UTC-7, Yaz Saito wrote:

Assume we have foo.example.com, whose value changes unpredictably.

1. Initially, the A record of foo.example.com points to, say 1.2.3.4.

2. Start a grpc client, with the server pointed at foo.example.com:10000. The client fails to

  connect since there's nothing running at 1.2.3.4:10000.

3. Start a grpc server at an IP address 1.2.3.5:10000. 

4. Update the DNS server so that foo.example.com points to 1.2.3.5.

In this situation, the grpc client never seems to discover the server at 1.2.3.5, even when I set the DNS TTL very short.

Am I diagnosing the problem correct? And if so, is there a way to work around?

--

yaz

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-Abhishek

[Craig Tiller]

The behavior is supposed to be that we periodically (with exponential back-off) retry resolution and then connection until we get a successful connection.

We currently rely on getaddrinfo to do the resolution, so we don't get any insight into the TTL on the dns entry - that's something we'll pick up soon though (with an optional embedding of c-ares).

Could you add a log line to blocking_resolve_address_impl() in resolve_address_posix.c and verify that we are in fact repeatedly calling this?

On Thu, Aug 18, 2016 at 4:20 PM Abhishek Parmar <abhi...@carbon3d.com> wrote:

(Replying for Yaz, he is on vacation)

On Thu, Aug 18, 2016 at 4:15 PM, <raut...@gmail.com> wrote:

Steps 4 and 5 should be interchanged I think.

You mean 3 and 4 should be swapped? I don't think it matters.

 

What does host foo.example.com results in, on your computer?

Are you running your code on a Linux box or some other environment?

It is running on linux.

Thanks,

On Wednesday, 17 August 2016 13:49:21 UTC-7, Yaz Saito wrote:

Assume we have foo.example.com, whose value changes unpredictably.

1. Initially, the A record of foo.example.com points to, say 1.2.3.4.

2. Start a grpc client, with the server pointed at foo.example.com:10000. The client fails to

  connect since there's nothing running at 1.2.3.4:10000.

3. Start a grpc server at an IP address 1.2.3.5:10000. 

4. Update the DNS server so that foo.example.com points to 1.2.3.5.

In this situation, the grpc client never seems to discover the server at 1.2.3.5, even when I set the DNS TTL very short.

Am I diagnosing the problem correct? And if so, is there a way to work around?

--

yaz

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-Abhishek

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[raut...@gmail.com]

What language is your client written in?
Java, C++ or Go?

For GO, there are two ways to get list of IP addresses for a FQDN Name.

IIRC, one of the implementations for resolver is via a syscall and other one is via a Go's stdlib.

You might want to double check on behavior if that is GO.

On Thursday, 18 August 2016 16:20:34 UTC-7, Abhishek Parmar wrote:

(Replying for Yaz, he is on vacation)

On Thu, Aug 18, 2016 at 4:15 PM, <raut...@gmail.com> wrote:

Steps 4 and 5 should be interchanged I think.

You mean 3 and 4 should be swapped? I don't think it matters.

 

What does host foo.example.com results in, on your computer?

Are you running your code on a Linux box or some other environment?

It is running on linux.

 

Thanks,

On Wednesday, 17 August 2016 13:49:21 UTC-7, Yaz Saito wrote:

Assume we have foo.example.com, whose value changes unpredictably.

1. Initially, the A record of foo.example.com points to, say 1.2.3.4.

2. Start a grpc client, with the server pointed at foo.example.com:10000. The client fails to

  connect since there's nothing running at 1.2.3.4:10000.

3. Start a grpc server at an IP address 1.2.3.5:10000. 

4. Update the DNS server so that foo.example.com points to 1.2.3.5.

In this situation, the grpc client never seems to discover the server at 1.2.3.5, even when I set the DNS TTL very short.

Am I diagnosing the problem correct? And if so, is there a way to work around?

--

yaz

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-Abhishek

[Craig Tiller]

(I'm assuming Node or C++ based on previous conversations with Yaz/Abhishek)

To view this discussion on the web visit https://groups.google.com/d/msgid/grpc-io/b7a72b7a-1d4c-4e7c-b016-508e0ac76841%40googlegroups.com.

[Abhishek Parmar]

This one is c++.

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-Abhishek

[Yaz Saito]

Sorry for delay. I just checked the behavior with grpc-1.0.0, and the things are working as expected. 

To view this discussion on the web visit https://groups.google.com/d/msgid/grpc-io/CAD2hskzrZsYV5y%3DoKWC6BKrXbwqAcM%2BFk0eZEu5Ftx0B%3DnBTTw%40mail.gmail.com.

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yaz