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Add DNS lookup plugin #1080

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6 changes: 6 additions & 0 deletions config/network-problem-monitor.json
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,12 @@
"reason": "ConntrackFull",
"path": "./config/plugin/network_problem.sh",
"timeout": "3s"
},
{
"type": "temporary",
"reason": "DNSUnreachable",
"path": "./config/plugin/dns_problem.sh",
"timeout": "3s"
}
]
}
24 changes: 24 additions & 0 deletions config/plugin/dns_problem.sh
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Original file line number Diff line number Diff line change
@@ -0,0 +1,24 @@
#!/bin/bash

# This plugin checks for dns network issues.

readonly OK=0
readonly NONOK=1
readonly UNKNOWN=2

readonly KUBERNETES_SERVICE='kubernetes.default'

# Check getent command is present
if ! command -v getent >/dev/null; then
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getent seems the most common tool available in a host, but do we want to use hosts or nslookup just in case getent is not available?

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I picked it since I assumed it would be the most available. I could change the logic to fall back to other tools, if getent isn't available?
May be in this order:

  1. getent
  2. host
  3. nslookup

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It will be good to know what install each tool in debian and red hat per example, I think gerent comes as part as libc so that makes it pretty common

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Using containers, and I don't know if that's a good idea:

Red Hat:

adrian@Adrians-MacBook-Pro:~$ docker run redhat/ubi10 getent hosts example.com
2600:1406:bc00:53::b81e:94c8 example.com
2600:1406:bc00:53::b81e:94ce example.com
2600:1408:ec00:36::1736:7f24 example.com
2600:1408:ec00:36::1736:7f31 example.com
2600:1406:3a00:21::173e:2e65 example.com
2600:1406:3a00:21::173e:2e66 example.com
adrian@Adrians-MacBook-Pro:~$ docker run redhat/ubi10 host example.com
docker: Error response from daemon: failed to create task for container: failed to create shim task: OCI runtime create failed: runc create failed: unable to start container process: error during container init: exec: "host": executable file not found in $PATH

Run 'docker run --help' for more information
adrian@Adrians-MacBook-Pro:~$ docker run redhat/ubi10 nslookup example.com
docker: Error response from daemon: failed to create task for container: failed to create shim task: OCI runtime create failed: runc create failed: unable to start container process: error during container init: exec: "nslookup": executable file not found in $PATH

Run 'docker run --help' for more information

Debian:

adrian@Adrians-MacBook-Pro:~$ docker run debian:latest getent hosts example.com
2600:1406:bc00:53::b81e:94c8 example.com
2600:1406:bc00:53::b81e:94ce example.com
2600:1408:ec00:36::1736:7f24 example.com
2600:1408:ec00:36::1736:7f31 example.com
2600:1406:3a00:21::173e:2e65 example.com
2600:1406:3a00:21::173e:2e66 example.com
adrian@Adrians-MacBook-Pro:~$ docker run debian:latest host example.com
docker: Error response from daemon: failed to create task for container: failed to create shim task: OCI runtime create failed: runc create failed: unable to start container process: error during container init: exec: "host": executable file not found in $PATH

Run 'docker run --help' for more information
adrian@Adrians-MacBook-Pro:~$ docker run debian:latest nslookup example.com
docker: Error response from daemon: failed to create task for container: failed to create shim task: OCI runtime create failed: runc create failed: unable to start container process: error during container init: exec: "nslookup": executable file not found in $PATH

Run 'docker run --help' for more information

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Seems getent is the way to go

echo "Could not find 'getent' - require getent"
exit $UNKNOWN
fi

# Return success if a DNS lookup to the Kubernetes host is successful
if getent hosts "${KUBERNETES_SERVICE}" >/dev/null; then
echo "DNS lookup to ${KUBERNETES_SERVICE} is working"
exit $OK
else
echo "DNS lookup to ${KUBERNETES_SERVICE} is not working"
exit $NONOK
fi