Cloudinit resets network scripts to default configuration DHCP once Config Drive is removed after sometime

[ubuntu-server-builder]

This bug was originally filed in Launchpad as LP: #1893770

Launchpad details

affected_projects = []
assignee = None
assignee_name = None
date_closed = None
date_created = 2020-09-01T11:18:55.806587+00:00
date_fix_committed = None
date_fix_released = None
id = 1893770
importance = medium
is_complete = False
lp_url = https://bugs.launchpad.net/cloud-init/+bug/1893770
milestone = None
owner = vradhakrishna
owner_name = vijayendra radhakrishna
private = False
status = in_progress
submitter = vradhakrishna
submitter_name = vijayendra radhakrishna
tags = []
duplicates = []

Launchpad user vijayendra radhakrishna(vradhakrishna) wrote on 2020-09-01T11:18:55.806587+00:00

Cloudinit version: 19.1
Platform: OpenStack based.
OS: RHEL, SUSE

We use config drive(/dev/sr0) as a data source to configure network interfaces in the guest but configdrive is not always available and may be removed after couple of hours from the hypervisor.

On a first boot cloudinit uses data provided in config drive and updates system level network scripts /etc/sysconfig/ifcfg-* (Static configuration of networks) files and also configures the interface in the guest.

As long as the configdrive is available, reboots will relay on system scripts for the configuring network but once configdrive is removed, datasource becomes None meaning it neither system script nor config drive

which makes cloud init to configure default network which is DHCP

[ubuntu-server-builder]

Launchpad user Ryan Harper(raharper) wrote on 2020-09-01T14:51:12.678196+00:00

Hello,
Thanks for filing a bug.

The config-drive provided to an instance includes metadata that provides and instance-id. If the config-drive is removed, cloud-init should not longer be active during subsequent boots. It sounds like cloud-init is not installed correctly.

Are you using official cloud-images from RHEL and SUSE? Have you manually enabled the cloud-init service files? Cloud-init will disable itself if there are not datasources detected.

Can you run cloud-init collect-logs and attach the generated tarball?

[ubuntu-server-builder]

Launchpad user Ryan Harper(raharper) wrote on 2020-09-01T14:51:20.381799+00:00

[ubuntu-server-builder]

Launchpad user Divya K Konoor(dikonoor) wrote on 2020-09-09T16:10:11.990832+00:00

cloud-init used here is not from RHEL or SUSE. As a next step, we will try validate if this behavior can be reproduced with cloud-init shipped with RHEL or SLES and see if this can be reproduced there.

[ubuntu-server-builder]

Launchpad user vijayendra radhakrishna(vradhakrishna) wrote on 2020-09-10T07:56:53.869899+00:00

We have tested the mentioned behavior on cloudint 19.4(RHEL provided cloudinit) on RHEL8.2 guest VM

Observing the same behaviors as explained. Attached the cloudinit log for your reference.

Please let me know if any other details are required.

Thanks.
Launchpad attachments: cloudinit log

[ubuntu-server-builder]

Launchpad user Scott Moser(smoser) wrote on 2020-09-10T12:32:07.941924+00:00

I'm pretty sure cloud-init is working as designed here.
Please see

• https://bugs.launchpad.net/ubuntu/+source/cloud-init/+bug/1888858
• boot.rst: add First Boot Determination section #568

for more information.

[ubuntu-server-builder]

Launchpad user Divya K Konoor(dikonoor) wrote on 2020-09-11T10:02:38.919104+00:00

While we look at the links provided by Scott above
(https://bugs.launchpad.net/cloud-init/+bug/1712680 from inside one of the above links has a lot of data), the current downstream patch that we are using to get past this issue is return from the below function is datasrc is found as None. This has worked for us so far.

at
https://github.com/canonical/cloud-init/blob/stable-19.4/cloudinit/stages.py#L678

def apply_network_config(self, bring_up):

  if ((self.datasource is NULL_DATA_SOURCE) or (
            self.datasource is None)):
        LOG.info("Data source is None. Skipping network config")
        return

    if self.datasource:
        try:
            if ((self.datasource.dsname == "None") or (
                    self.datasource.dsname is "None") or (
                        self.datasource.dsname is None)):
                LOG.info(
                    "Data source is an instance of DataSourceNone. "
                    "Skipping network config")
                return
        except BaseException:
            LOG.info("in except block")
            if (isinstance(self.datasource, dsnone.DataSourceNone)):
                LOG.info(
                    "Data source is an instance of DataSourceNone. "
                    "Skipping network config")
                return

[ubuntu-server-builder]

Launchpad user Eduardo Otubo(otubo) wrote on 2020-09-15T10:11:29.912740+00:00

From RHEL and Openstack point of view, we never remove the config-drive and that's the reason we never faced this issue. Keeping the config-drive attached is an option for you, Divya?

Also, if you could paste a diff-style code it would be much easier to review, or even better a github link with the colored diff.

[ubuntu-server-builder]

Launchpad user Eduardo Otubo(otubo) wrote on 2020-09-17T12:19:10.603790+00:00

Just found out other similar bugs related to this behavior and this is fixed downstream only. The bug wasn't exactly on cloud-init, but looks like we were not including ds-identify on the rpm, causing the issue. Please give it a try on any RHEL shipped rpms >= cloud-init-18.5-5.*

[ubuntu-server-builder]

Launchpad user Divya K Konoor(dikonoor) wrote on 2020-09-17T12:38:19.570764+00:00

Edurado, ok. I think we have tried it with the RHEL cloud-init 8.5 that was getting shipped with RHEL8 and could reproduce is but we will try it and get back.

We did take a look at why we have a need to remove the data source and due to some reasons specific to our platform/environment, we have a need to remove the datasource. I believe cloud-init should accomodate both cases- with and without datasource. In a case there is no datasource, cloud-init should not go and reset NW to dhcp.

[ubuntu-server-builder]

Launchpad user Ryan Harper(raharper) wrote on 2020-09-17T14:50:27.833432+00:00

In a case there is no datasource, cloud-init should not go and reset NW to dhcp.

If there is no datasource, cloud-init does not run. If you've removed your datasource, cloud-init should no longer activate during boot. In your case, you've removed your datasource so cloud-init attempts to look for one. On Power architecture, cloud-init cannot detect if it's running on Openstack without trying to contact the metadata service due to limitations in the Nova/PowerVM.

https://cloudinit.readthedocs.io/en/latest/topics/datasources/openstack.html

cloud-init then attempts to contact OpenStack over the network, it does this by making a best guess on which network interface to bring up, run DHCP and attempt to contact the metadata service.

Command: ['/var/tmp/cloud-init/cloud-init-dhcp-2zup00qk/dhclient', '-1', '-v', '-lf', '/var/tmp/cloud-init/cloud-init-dhcp-2zup00qk/dhcp.leases', '-pf', '/var/tmp/cloud-init/cloud-init-dhcp-2zup00qk/dhclient.pid', 'env32', '-sf', '/bin/true']
Exit code: 2
Reason: -
Stdout:
Stderr: Internet Systems Consortium DHCP Client 4.3.6
Copyright 2004-2017 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

    Listening on LPF/env32/fa:c9:e6:d2:01:20
    Sending on   LPF/env32/fa:c9:e6:d2:01:20
    Sending on   Socket/fallback
    Created duid "\000\004\220\007\237\263\032[K\023\261\364}\206\256\275Jc".
    DHCPDISCOVER on env32 to 255.255.255.255 port 67 interval 4 (xid=0xde2eb608)
    DHCPDISCOVER on env32 to 255.255.255.255 port 67 interval 9 (xid=0xde2eb608)
    DHCPDISCOVER on env32 to 255.255.255.255 port 67 interval 18 (xid=0xde2eb608)
    DHCPDISCOVER on env32 to 255.255.255.255 port 67 interval 19 (xid=0xde2eb608)
    DHCPDISCOVER on env32 to 255.255.255.255 port 67 interval 11 (xid=0xde2eb608)
    No DHCPOFFERS received.
    Unable to obtain a lease on first try.  Exiting.

Since cloud-init cannot reach the OpenStack metadata service, it does not have an instance-id so it will assume this boot is a first boot. On first boot, without network configuration from Openstack cloud-init will render a fallback network config, dhcp on best guess interface, which is why you see a change in network configuration.

The core issues are:

1. OpenStack Nova on Power does not have a way to indicate to the guest that it's running on Openstack; on x86 and arm, this is done via smbios/dmi tables; there is not yet an implementation for Power

2. When you remove your provided datasource (/dev/srX) you've removed the metadata that indicated cloud-init has already been booted.

As Scott mentioned, to address (2), you can look at configuring the manual-cache-clean option which will configure cloud-init in way as to keep existing metadata changes in place until the user manually cleans out cloud-init metadata.

[ubuntu-server-builder]

Launchpad user Eduardo Otubo(otubo) wrote on 2020-10-01T14:18:23.795388+00:00

@ryan, I have a question about:

If there is no datasource, cloud-init does not run. If you've removed your datasource, cloud-init

If cloud-init doesn't run, it shouldn't look for datasources, is that correct?

should no longer activate during boot. In your case, you've removed your datasource so cloud-init
attempts to look for one. On Power architecture, cloud-init cannot detect if it's running on
Openstack without trying to contact the metadata service due to limitations in the Nova/PowerVM.

[ubuntu-server-builder]

Launchpad user Ryan Harper(raharper) wrote on 2020-10-01T15:00:22.726801+00:00

@eduardo

@ryan, I have a question about:

If there is no datasource, cloud-init does not run. If you've removed your datasource, cloud-init

If cloud-init doesn't run, it shouldn't look for datasources, is that correct?

cloud-init won't run if ds-identify does not detect a datasource.

On each boot cloud-init's systemd generator calls ds-identify. This program runs to determine whether cloud-init should run or not. The ds-identify default policy is to search, and report that cloud-init should run if:

1. it finds a datasource
2. if there might be a datasource

For (1); cloud-init examines specific values on the system, files in a
directory, values in system UUID, etc... these types of checks are binary;
we either have the correct value or we don't.

For (2); in some cases, ds-identify cannot be 100% sure the datasource isn't
present because the platform on which we're running does not provide us with
the needed data.

For POWER systems which do not export DMI values, the OpenStack Datasource
will always return maybe as the only way to know is to bring up networking and
query the OpenStack metadata service.

Contrast this with x86 platform where OpenStack VMs export values in the DMI
table. ds-identify can check the value of the dmi product name and know for
sure whether it's running on OpenStack or not.

ds-identify then writes out its conclusions in /run/cloud-init/cloud.cfg
and enables the cloud-init.target which will run the 4 stages of cloud-init.

For this bug, on first boot, /dev/sr1 included an OpenStack ConfigDrive, so
ds-identify reports:

cat /run/cloud-init/cloud.cfg

datasource_list: [ ConfigDrive, None ]

The configdrive payload includes a network configuration which was applied.
After some time, the iso in /dev/sr1 was removed and the node in question
was rebooted. On the next boot when ds-identify runs and does not find
ConfigDrive in /dev/sr1. When checking for OpenStack datasources ds-identify
will report 'maybe' since the arch is not x86. This results in the
following cloud.cfg

cat /run/cloud-init/cloud.cfg

datasource_list: [ OpenStack, None ]

Now, cloud-init OpenStack datasource starts, and because the system currently
lacks the original ConfigDrive datasource, including the instance-id, this
looks like a brand new boot; and cloud-init will then bring up ephemeral
networking DHCP, attempt to see if there is an OpenStack metadata server
on the network (there is not, see the logs); and it then proceeds to using
DataSourceNone which is really a fallback datasource which tries it's best
to be useful but ultimately isn't what folks really need.

[ubuntu-server-builder]

Launchpad user vijayendra radhakrishna(vradhakrishna) wrote on 2020-10-09T09:27:14.768702+00:00

I have explored a bit on manual_cache_clean: true option suggested, Here are some of the findings.

1. Some of the capture use case has broken as this requires this manual cleaup on VMs as per documentation mentioned here.
   https://cloudinit.readthedocs.io/en/latest/topics/boot.html#not-present

2. In case if you have very large number of VMs this becomes overhead to do manual cleanup for all capture use cases

3. It also has security concerns when ssh-key rotation doesn't happen for capture use case where cleanup has not performed