Istio FAQ: failed to resolve after enabling smart DNS

This article excerpts from istio Learning notes

Problem description

When enabled istio Of Smart DNS ( intelligence DNS) after , We found that in some cases DNS Parse failure , such as :

• be based on alpine In container resolution of the image dns Failure .
• grpc Service parsing dns Failure .

reason

Smart DNS There are some problems in the initial implementation , Responsive DNS The packet format is the same as that of the normal DNS There are some differences , Go to the bottom storehouse glibc No problem with parsing , But use other dns The client may fail :

• alpine Mirror the underlying library to use musl libc, Analytic behavior is similar to glibc It's a little bit different ,musl libc In this case, the abnormal packet format will lead to the failure of parsing , Most applications use the underlying library to parse , Most applications fail to parse .
• be based on c/c++ Of grpc Framework Services ,dns Parsing defaults to c-ares library , There is no system call to allow the underlying library to parse ,c-ares In this packet exception , Some scenarios will fail to parse .

Repair

stay istio 1.9.2 Time to fix this problem , Reference key PR #31251 And one of them issue .

avoid

If the upgrade is temporarily unavailable istio To 1.9.2 above , You can avoid it in the following ways :

• The basic image is from alpine Mirror to another mirror ( The underlying libraries of other basic images are basically glibc).
• c/c++ Of grpc service , Appoint GRPC_DNS_RESOLVER The environment variable is native, It means that the underlying library is used for parsing , Don't go by default c-ares library . Environment variable interpretation reference GRPC Official documents .