poor DNS response can hang host processes

[jrcheli]

bin/linux/scope run -c tcp://bogushost:10090 -- /bin/echo something takes 45 seconds to actually get "something" to the local console. And then it takes another 30 seconds or so for the process to exit.

This was observed on a machine where nslookup of bogushost was very slow.

cribl@ubuntu18_4:~/appscope$ time nslookup bogushost
;; connection timed out; no servers could be reached

real	0m15.019s
user	0m0.009s
sys	0m0.006s

What surprised me most was the delay in getting console output to the screen. I think this must be a library issue, I'm seeing the same results for LD_PRELOAD=lib/linux/libscope.so SCOPE_CRIBL=tcp://bogushost:10090 /bin/echo something

[jrcheli]

cribl@ubuntu18_4:~/appscope$ systemd-resolve --status
Global
          DNSSEC NTA: 10.in-addr.arpa
                      16.172.in-addr.arpa
                      168.192.in-addr.arpa
                      17.172.in-addr.arpa
                      18.172.in-addr.arpa
                      19.172.in-addr.arpa
                      20.172.in-addr.arpa
                      21.172.in-addr.arpa
                      22.172.in-addr.arpa
                      23.172.in-addr.arpa
                      24.172.in-addr.arpa
                      25.172.in-addr.arpa
                      26.172.in-addr.arpa
                      27.172.in-addr.arpa
                      28.172.in-addr.arpa
                      29.172.in-addr.arpa
                      30.172.in-addr.arpa
                      31.172.in-addr.arpa
                      corp
                      d.f.ip6.arpa
                      home
                      internal
                      intranet
                      lan
                      local
                      private
                      test

Link 2 (ens33)
      Current Scopes: DNS
       LLMNR setting: yes
MulticastDNS setting: no
      DNSSEC setting: no
    DNSSEC supported: no
         DNS Servers: 192.168.88.2
          DNS Domain: localdomain