Weave Scope queries repeatedly for DNS name "true"

[bergtwvd]

I start Weave Scope as per instructions on https://www.weave.works/documentation/scope-latest-installing with:

version: '2'

services:
 scope:
  image: weaveworks/scope
  command:
  - "--probe.docker"
  - "true"
  privileged: true
  container_name: weavescope
  network_mode: "host"
  pid: "host"
  volumes:
  - /var/run/docker.sock:/var/run/docker.sock
  restart: always

When I do sudo tcpdump -v port 53 -i eth0 I see the following DNS messages.

13:28:40.762241 IP (tos 0x0, ttl 64, id 56717, offset 0, flags [DF], proto UDP (17), length 57)
    xxxx.51772 > yyyy: 23616+ AAAA? true.tno.nl. (29)
13:28:40.762319 IP (tos 0x0, ttl 64, id 56718, offset 0, flags [DF], proto UDP (17), length 57)
    xxxx.49673 > yyyy: 63954+ A? true.tno.nl. (29)
13:28:40.764365 IP (tos 0x0, ttl 125, id 17841, offset 0, flags [none], proto UDP (17), length 122)
    yyyy > xxxx.49673: 63954 NXDomain 0/1/0 (94)
13:28:40.764393 IP (tos 0x0, ttl 125, id 17842, offset 0, flags [none], proto UDP (17), length 122)
    yyyy > xxxxl.51772: 23616 NXDomain 0/1/0 (94)
13:28:40.764588 IP (tos 0x0, ttl 64, id 56719, offset 0, flags [DF], proto UDP (17), length 50)
    xxxx.49528 > yyyy: 26105+ AAAA? true. (22)
13:28:40.765360 IP (tos 0x0, ttl 64, id 56720, offset 0, flags [DF], proto UDP (17), length 50)
    xxxx.50258 > yyyy: 22506+ A? true. (22)
13:28:40.770368 IP (tos 0x0, ttl 125, id 17845, offset 0, flags [none], proto UDP (17), length 50)
    yyyy > xxxx.49528: 26105 ServFail 0/0/0 (22)
....

My company's DNS server is "bombarded" with these DNS queries, because this goes on forever.

How can thsi be resolved?
What is the meaning of the option "true" in the container command?

[2opremio]

Our bad, it should be "--probe.docker=true", in a single line.

I will make sure this is fixed.

[bergtwvd]

Ok, that is clarified 👍

Related question - while on topic - : how can a list of hostnames be passed into scope (i.e. where peer scope instances run) ? And/or will scope discover these itself in case Weave networking is used?

[2opremio]

how can a list of hostnames be passed into scope (i.e. where peer scope instances run) ?

I am not sure I understand what you mean. Can you please clarify?

will scope discover these itself in case Weave networking is used.

Yes, it will

[bergtwvd]

In scope launch I can add a list of IP addresses. Where can I put that list in the Compose file?

[bergtwvd]

I see that the issue is closed, but still some follow up:

I still see that scope repeatedly queries the DNS server (roughly every 10s) for the hostnames I provided in the compose file. Doesn't scope cache the IP addresses, so it only has to query once?

Compose file:

services:
 scope:
  image: weaveworks/scope
  command: --probe.docker=true app-docker01 app-docker02 app-docker03 app-docker04 app-docker05
  privileged: true
  container_name: weavescope
  network_mode: "host"
  pid: "host"
  volumes:
  - /var/run/docker.sock:/var/run/docker.sock
  restart: always

[2opremio]

In scope launch I can add a list of IP addresses. Where can I put that list in the Compose file?

At the end of the command section (where "true" was incorrectly placed)

version: '2'

services:
 scope:
  image: weaveworks/scope
  command:
  - "--probe.docker=true"
  - <target1>
  - <target2>
  - <target3>
  privileged: true
  container_name: weavescope
  network_mode: "host"
  pid: "host"
  volumes:
  - /var/run/docker.sock:/var/run/docker.sock
  restart: always

Doesn't scope cache the IP addresses, so it only has to query once?

Querying repeatedly is intentional. 10s seems reasonable, why is that a problem?

[bergtwvd]

It eats away some CPU time and networking comms, which is not needed if you would cache the IP address after the first query. Hosts won't change IP address that quickly.

And my company's system admin was actually complaining :-).

[2opremio]

It eats away some CPU time and networking comms

That should be negligible

And my company's system admin was actually complaining

What was the complaint exactly? Was he annoyed by the traffic?

[bergtwvd]

Yep :-).