[Bug 1636912] Re: systemd-networkd runs too late for cloud-init.service (net)

[Ryan Harper]

On Thu, Oct 27, 2016 at 3:57 PM, Martin Pitt <martin.pitt at ubuntu.com>
wrote:

> > cloud-init expects networking to be up, like 'networking.service'
> before it runs..
>
>
> I think it needs to make up its mind -- why does it want to run
> Before=network-online.target then? I thought the idea was that cloud-init
> is able to *provide* a network configuration (through the YAML). It seems
> to me that this might have to be split into two parts then -- one that can
> provide network config which runs early and does not require networking,
> and one that can use the network to configure other bits?
>

we have to do both.

In the case that we have a local config which provides networking
configuration, we can emit it, and then we want to "bring it up"

In other cases, we may need to bring up fallback networking (ie, dhcp on
eth0) to look for a metadata service on the network
which also may provide network configuration (which we writeout) and then
want to "bring it up"


>
> > So why shouldn't we use networkd-wait-online ?
>
> You can use the program. I said that it might not be the best idea to
> use After=s-n-wait-online.service, as that would block the entire cloud-
> init.service and with it the entire boot (as cloud-init.service has very
> strong dependencies) if there is no network available.
>

cloud-init.service *requires* network; it's designed to block until then
otherwise
you just timeout trying to reach network endpoints like Openstack metadata
service.

The "hang" in UbuntuCore was primarily related to *not* providing a nocloud
seed
in the image;  when it was booted without a seed and not disabled, it goes
an *looks* for a seed, first local, then over the net.


>
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> https://bugs.launchpad.net/bugs/1636912
>
> Title:
>   systemd-networkd runs too late for cloud-init.service (net)
>
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https://bugs.launchpad.net/bugs/1636912

Title:
  systemd-networkd runs too late for cloud-init.service (net)

Status in systemd:
  Unknown
Status in cloud-init package in Ubuntu:
  Triaged
Status in systemd package in Ubuntu:
  Triaged
Status in cloud-init source package in Xenial:
  New
Status in systemd source package in Xenial:
  Triaged

Bug description:
  Ubuntu Core 16 images using cloud-init fail to function when the
  DataSource is over the network (Like OpenStack) as networking is not
  yet available when cloud-init.service runs.

  cloud-init service unit deps look like this:

  [Unit]
  Description=Initial cloud-init job (metadata service crawler)
  DefaultDependencies=no
  Wants=cloud-init-local.service
  Wants=local-fs.target
  Wants=sshd-keygen.service
  Wants=sshd.service
  After=cloud-init-local.service
  After=networking.service
  Requires=networking.service
  Before=basic.target
  Before=dbus.socket
  Before=network-online.target
  Before=sshd-keygen.service
  Before=sshd.service
  Before=systemd-user-sessions.service
  Conflicts=shutdown.target

  Here's networkd unit deps:

  [Unit]
  Description=Network Service
  Documentation=man:systemd-networkd.service(8)
  ConditionCapability=CAP_NET_ADMIN
  DefaultDependencies=no
  # dbus.service can be dropped once on kdbus, and systemd-udevd.service can be
  # dropped once tuntap is moved to netlink
  After=systemd-udevd.service dbus.service network-pre.target systemd-sysusers.service systemd-sysctl.service
  Before=network.target multi-user.target shutdown.target
  Conflicts=shutdown.target
  Wants=network.target

  # On kdbus systems we pull in the busname explicitly, because it
  # carries policy that allows the daemon to acquire its name.
  Wants=org.freedesktop.network1.busname
  After=org.freedesktop.network1.busname

  
  And a critical-chain output:

  root at snap-test7:~# systemd-analyze critical-chain systemd-networkd
  Failed to get ID: Unit name systemd-networkd is not valid.
  The time after the unit is active or started is printed after the "@" character.
  The time the unit takes to start is printed after the "+" character.

  root at snap-test7:~# systemd-analyze critical-chain systemd-networkd.service
  The time after the unit is active or started is printed after the "@" character.
  The time the unit takes to start is printed after the "+" character.

  systemd-networkd.service +440ms
  └─dbus.service @11.461s
    └─basic.target @11.403s
      └─sockets.target @11.401s
        └─dbus.socket @11.398s
          └─cloud-init.service @10.127s +1.266s
            └─networking.service @9.305s +799ms
              └─network-pre.target @9.295s
                └─cloud-init-local.service @3.822s +5.469s
                  └─local-fs.target @3.813s
                    └─run-cgmanager-fs.mount @12.687s
                      └─local-fs-pre.target @1.393s
                        └─systemd-tmpfiles-setup-dev.service @1.116s +195ms
                          └─kmod-static-nodes.service @887ms +193ms
                            └─system.slice @783ms
                              └─-.slice @721ms

  
  cloud-init would need networkd to run at or before 'networking.service' so it can raise networking to then find and use network-based datasources.

  # grep systemd /usr/share/snappy/dpkg.list 
  ii  libnss-resolve:amd64          229-4ubuntu11                                            amd64        nss module to resolve names via systemd-resolved
  ii  libpam-systemd:amd64          229-4ubuntu11                                            amd64        system and service manager - PAM module
  ii  libsystemd0:amd64             229-4ubuntu11                                            amd64        systemd utility library
  ii  systemd                       229-4ubuntu11                                            amd64        system and service manager
  ii  systemd-sysv                  229-4ubuntu11                                            amd64        system and service manager - SysV links

  # grep cloud-init /usr/share/snappy/dpkg.list 
  ii  cloud-init                    0.7.8-201610260005-gf7a5756-0ubuntu1~trunk~ubuntu16.04.1 all          Init scripts for cloud instances

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