[jira] [Resolved] (CLOUDSTACK-5986) dnsmasq racy condition result in dnsmasq failed to handout IP address

["Sheng Yang (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CLOUDSTACK-5986?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Sheng Yang resolved CLOUDSTACK-5986.
------------------------------------

    Resolution: Fixed

> dnsmasq racy condition result in dnsmasq failed to handout IP address
> ---------------------------------------------------------------------
>
>                 Key: CLOUDSTACK-5986
>                 URL: https://issues.apache.org/jira/browse/CLOUDSTACK-5986
>             Project: CloudStack
>          Issue Type: Bug
>      Security Level: Public(Anyone can view this level - this is the default.) 
>          Components: Virtual Router
>    Affects Versions: 4.2.0, 4.2.1
>            Reporter: Sheng Yang
>            Assignee: Sheng Yang
>            Priority: Critical
>             Fix For: 4.2.1, 4.3.0
>
>
> In the past, dnsmasq.leases is managed by cloudstack, and would be updated after new entry is added(and the entry with same IP or host would be removed).
> In 4.2, we introduced dhcp_release try to speed up the dnsmasq reload process, thus result in this issue.
> So in this scenario:
> 1. VM1 would create entry: "mac A, IP A, host A"
> 2. VM2 would create entry: "mac B, IP B, host B"
> 3. VM1 destroyed and VM 2 destroyed, no change to lease file, two records still existed.
> 4. VM1 created with IP B: "mac C, IP B, host A".
> At this time, lease file would only contain: "mac C, IP B, host A", because the original entries would be removed by either IP match or host name match.
> In fact dnsmasq still holds lease of IP A with mac A in memory, but record is already removed from lease file by cloudstack. The lease file is out of sync now.
> 5. VM2 recreated with IP A, dhcp_release would be used to release the lease. But there is no "mac A, IP A" record in the lease file, so dhcp_release failed.
> So result in dnsmasq cannot handle out the IP A to new mac D, because dnsmasq was still holding lease for IP A with mac A and haven't been released yet.
> So it only happened when user create and destroy different VMs which share the same name but get different IPs.



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