[lxc-devel] [CRIU] LXC live migrate

[Pavel Emelyanov]

On 11/27/2013 01:58 PM, Daniel Lezcano wrote:
> On 11/27/2013 09:54 AM, Pavel Emelyanov wrote:
>> On 11/27/2013 06:19 AM, Qiang Huang wrote:
>>> On 2013/11/27 0:19, Marian Marinov wrote:
>>>> On my test setup it works for processes like apache, dovecot and mysql.
>>>>
>>>> However it does not work with containers:
>>>>
>>>> root at s321:~# criu dump -D deb1 -t 19332 --file-locks
>>>> (00.004962) Error (namespaces.c:155): Can't dump nested pid namespace for 28352
>>>> (00.004985) Error (namespaces.c:321): Can't make pidns id
>>>> (00.005327) Error (cr-dump.c:1811): Dumping FAILED.
>>>> root at s321:~#
>>>> When I try to dump the init process(which I believe I should not do), here is what I see:
>>>>     http://pastebin.com/DFC0ADpp
>>>>
>>>> (00.291294) Error (tty.c:222): tty: Unexpected format on path /dev/tty1
>>>> (00.291315) Error (cr-dump.c:1491): Dump files (pid: 29702) failed with -1
>>>> (00.291892) Error (cr-dump.c:1811): Dumping FAILED.
>>>>
>>>> This is my setup:
>>>> 19332 ?        Ss     0:00 lxc-start -n deb1 -d
>>>> 28352 ?        Ss     0:00  \_ init [3]
>>>> 28393 ?        Ss     0:00      \_ /usr/sbin/apache2 -k start
>>>> 28419 ?        S      0:00      |   \_ /usr/sbin/apache2 -k start
>>>> 28422 ?        Sl     0:00      |   \_ /usr/sbin/apache2 -k start
>>>> 28423 ?        Sl     0:00      |   \_ /usr/sbin/apache2 -k start
>>>> 28489 ?        S      0:00      \_ /bin/sh /usr/bin/mysqld_safe
>>>> 28620 ?        Sl     0:00      |   \_ /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/mysql --user=mysql
>>>> --pid-file=/var/run/mysqld/mysqld.pid --socket=/var/run/mysqld/mysqld.sock --port
>>>> 28621 ?        S      0:00      |   \_ logger -t mysqld -p daemon.error
>>>> 28598 ?        Ss     0:00      \_ /usr/sbin/sshd
>>>> 29702 pts/0    Ss+    0:00      \_ /sbin/getty 38400 tty1 linux
>>>>
>>>> I rebooted the container without getty on tty1 and then I got this:
>>>>
>>>> (00.260757) Error (mount.c:255): 86:/dev/tty4 doesn't have a proper root mount
>> This is the reason. That's container's console which is a bind mounted tty from
>> the host. And since this is an external connection, CRIU doesn't dump one.
>>
>> There are two ways to resolve this. The first is disable container's console. It's
>> fast, but ugly. The second way is supporting one, but it would require criu hacking.
>> We should detect, that this is an external tty, decide, that we're OK to disconnect
>> it after dump and on restore -- connect it back.
> 
> The third one would be to implement lxc-checkpoint and lxc-restart 
> (which are empty) to invoke CRUI. Then from there you can dump the 
> container's configuration and restart with.

Yes, it's also possible and probably easier. But as far as the console is concerned,
some patching on the criu code will still be needed.

Thanks,
Pavel