The sdk should auto-detect ipv4 loopback and ipv6 loopback for daprd communication.

[LMWF]

Expected Behavior

Today the sdk will choose the ipv4 loopback address to contact darpd: 127.0.0.1 (this was changed from "localhost" today). Some users may prefer ipv6 or may operate in an ipv6 only environment. The sdk should automatically detect which one to use: ipv6 or ipv4.

Actual Behavior

Today the sdk will always use the ipv4 loopback address: 127.0.0.1 to connect to daprd.

[yaron2]

Might be better to detect the environment automatically and set the address accordingly. This is a detail the user shouldn't be aware of.

[amanbha]

While reducing the friction because of issues faced by localhost is good. Asking user to provide this ipv4(or ipv6)address is not good solution, I agree it should be auto discovered for user.

[artursouza]

@amanbha @yaron2 I agree for auto-detection. It would be interesting to see how the auto-detection can be done without causing delay (waiting for IPV6 connection to fail, for example).

[yaron2]

A delay on startup is a non-issue.

[artursouza]

@yaron2 If it is "small", I agree.

[yaron2]

Looks like Java has this built in: https://docs.oracle.com/javase/7/docs/api/java/net/InetAddress.html#getLoopbackAddress%28%29

[LMWF]

Doesn't it have to use the one daprd is using? Can't daprd be using the ipv6 loopback, and that api returns the ipv4 loopback?

[artursouza]

I thought about it too. If both are present, client must use what dapr is using - which can only be known by trying to connect.

[willtsai]

/assign

[willtsai]

I have made an investigation pass into this issue and have the following findings:

• A constant called SIDECAR_IP has since been added as a part of https://github.com/dapr/java-sdk/pull/333/, which is implemented to detect the sidecar's IP address by inspecting the system properties via a call to Properties.SIDECAR_IP.get() that looks for the sidecar's IP using this logic: first try to get system property named "dapr.sidecar.ip", if not available try get environment variable named "DAPR_SIDECAR_IP", and if neither is available fallback to "DEFAULT_SIDECAR_IP" which is hardcoded to "127.0.0.1"
• Given the above, I think that these points that were raised are now already addressed: -- "Doesn't it have to use the one daprd is using? Can't daprd be using the ipv6 loopback, and that api returns the ipv4 loopback?" -- "If both are present, client must use what dapr is using - which can only be known by trying to connect."

Thus, I believe the remaining work for this issue would be as follows:

1. Refactor the source code and tests to change the currently hardcoded "127.0.0.1" to use the value from Properties.SIDECAR_IP.get() instead.
2. Change the DEFAULT_SIDECAR_IP constant's value from the hardcoded "127.0.0.1" to instead use the Java API getLoopbackAddress that @yaron2 suggested instead. This would make the IP default value more dynamic and account for situations where users operate in an exclusively ipv6 environment and the logic ends up falling back to the default value.

@artursouza - thoughts on the above? If you think this is the right approach, I can start working on these changes.

[artursouza]

I've just looked at the current code in master for runtime and this is the default behavior of the sidecar:

• Standalone mode: listen to all addresses
• K8s mode: listen to [::1],127.0.0.1

So, this approach is fine as of now. Let's keep it. User can override this setting if he/she decided to override the default listen ports.

[willtsai]

@artursouza - awesome, thanks for looking into this. I'd like to confirm here before proceeding:

1. Are you saying that the approach of setting DEFAULT_SIDECAR_IP to the loopback address via InetAddress.getLoopbackAddress() is fine?
2. Or are you thinking we need to set DEFAULT_SIDECAR_IP to the localhost address via InetAddress.getLocalHost()?

Given the default behavior of the sidecar you've determined, I believe that Option 1 would be the correct approach given that it listens to the loopback addresses in K8s mode. Please let me know if you also agree with Option 1, thanks!

[willtsai]

@artursouza - awesome, thanks for looking into this. I'd like to confirm here before proceeding:

1. Are you saying that the approach of setting DEFAULT_SIDECAR_IP to the loopback address via InetAddress.getLoopbackAddress() is fine?
2. Or are you thinking we need to set DEFAULT_SIDECAR_IP to the localhost address via InetAddress.getLocalHost()?

Given the default behavior of the sidecar you've determined, I believe that Option 1 would be the correct approach given that it listens to the loopback addresses in K8s mode. Please let me know if you also agree with Option 1, thanks!

Update: After reading your feedback again @artursouza I've gone ahead with Option 1 using InetAddress.getLoopbackAddress() - please see https://github.com/dapr/java-sdk/pull/649 for latest implementation.