[Gluster-users] Where does Gluster capture the hostnames from?
TomK
tomkcpr at mdevsys.com
Tue Sep 24 01:31:19 UTC 2019
Hey All,
My hosts below:
[root at mdskvm-p01 ~]# cat /etc/hosts
127.0.0.1 localhost localhost.localdomain localhost4
localhost4.localdomain4
::1 localhost localhost.localdomain localhost6
localhost6.localdomain6
[root at mdskvm-p01 ~]# hostname
mdskvm-p01.nix.mds.xyz
[root at mdskvm-p01 ~]# hostname -f
mdskvm-p01.nix.mds.xyz
[root at mdskvm-p01 ~]#
[root at mdskvm-p02 ~]# cat /etc/hosts
127.0.0.1 localhost localhost.localdomain localhost4
localhost4.localdomain4
::1 localhost localhost.localdomain localhost6
localhost6.localdomain6
[root at mdskvm-p02 ~]# hostname
mdskvm-p02.nix.mds.xyz
[root at mdskvm-p02 ~]# hostname -f
mdskvm-p02.nix.mds.xyz
[root at mdskvm-p02 ~]#
My take on the /etc/hosts file discussion:
1) If hostname / hostname -f returns any valid values, the software
should capture it.
2) There is no benefit or need to use /etc/hosts in a small setup.
Larger setups resolving hosts against an enterprise DNS behind many
switches could be a problem. Managing our /etc/hosts files using
Ansible helped to reduce some of these problems esp since lookups are
logged against the connection tracking tables, that can get full,
network response time could vary etc. ("Semi static" I guess might
describe this approach best?) These are populated, if changes are
needed, via an initial DNS lookup once a day. Invariably, managing
/etc/hosts is time consuming and messy.
3) Running a good DNS cluster, something like a two node IPA cluster
that I run for a small setup, prevents such outages. This particularly
when also placing a VIP across the nodes and locating cluster nodes
across different hardware and locations.
4) Point 2) should be no reason why an application cannot obtain or
resolve proper DNS entries in 1).
Having said that, decided to check if there's any benefit to having
entries in /etc/hosts:
[root at mdskvm-p01 ~]# time $(dig mdskvm-p01.nix.mds.xyz >/dev/null)
real 0m0.092s
user 0m0.087s
sys 0m0.005s
[root at mdskvm-p01 ~]# time $(dig mdskvm-p02.nix.mds.xyz >/dev/null)
real 0m0.092s
user 0m0.084s
sys 0m0.008s
[root at mdskvm-p01 ~]# cat /etc/hosts
127.0.0.1 localhost localhost.localdomain localhost4
localhost4.localdomain4
::1 localhost localhost.localdomain localhost6
localhost6.localdomain6
192.168.0.60 mdskvm-p01.nix.mds.xyz mdskvm-p01
192.168.0.39 mdskvm-p02.nix.mds.xyz mdskvm-p02
[root at mdskvm-p01 ~]# vi /etc/hosts
[root at mdskvm-p01 ~]# time $(dig mdskvm-p01.nix.mds.xyz >/dev/null)
real 0m0.093s
user 0m0.082s
sys 0m0.010s
[root at mdskvm-p01 ~]# time $(dig mdskvm-p02.nix.mds.xyz >/dev/null)
real 0m0.093s
user 0m0.085s
sys 0m0.007s
[root at mdskvm-p01 ~]# time $(dig mdskvm-p01.nix.mds.xyz >/dev/null)
real 0m0.094s
user 0m0.084s
sys 0m0.010s
[root at mdskvm-p01 ~]# time $(dig mdskvm-p02.nix.mds.xyz >/dev/null)
real 0m0.092s
user 0m0.081s
sys 0m0.011s
[root at mdskvm-p01 ~]# cat /etc/hosts
127.0.0.1 localhost localhost.localdomain localhost4
localhost4.localdomain4
::1 localhost localhost.localdomain localhost6
localhost6.localdomain6
[root at mdskvm-p01 ~]#
So with /etc/hosts file entries present makes little difference in small
setup when governed by /etc/nsswitch.conf .
Having entries in /etc/hosts, doesn't affect how gluster displays the
entries when calling gluster volume status .
Cheers,
TK
On 9/23/2019 11:36 AM, Joe Julian wrote:
> Perhaps I misread the intent, I apologize if I did. I read "static
> entries" as "ip addresses" which I've seen suggested (from my
> perspective) far too often. /etc/hosts is a valid solution that can
> still adapt if the network needs to evolve.
>
> On 9/23/19 8:29 AM, ROUVRAIS Cedric wrote:
>> Hello,
>>
>> I guess everyone sort of has his perspective on this topic.
>>
>> I don't want to take this thread on an off-topic conversation
>> (discussing the merits of having a local hosts file) but I do dissent,
>> and therefore had to respond, on the shortcut that using a local
>> etc/host file creates a fixed network configuration that can never
>> adapt as business needs change. I'm running a k8s infrastructure and
>> actually have local conf files, FWIW.
>>
>> Regards,
>>
>> Cédric
>>
>>
>> -----Original Message-----
>> From: gluster-users-bounces at gluster.org
>> <gluster-users-bounces at gluster.org> On Behalf Of Joe Julian
>> Sent: lundi 23 septembre 2019 17:06
>> To: gluster-users at gluster.org
>> Subject: Re: [Gluster-users] Where does Gluster capture the hostnames
>> from?
>>
>> I disagree about it being "best practice" to lock yourself in to a
>> fixed network configuration that can never adapt as business needs
>> change.
>> There are other resilient ways of ensuring your hostnames resolve
>> consistently (so that your cluster doesn't run loose ;-)).
>>
>> On 9/23/19 7:38 AM, Strahil wrote:
>>> Also,
>>>
>>> It's more safe to have static entries for your cluster - after all if
>>> DNS fails for some reason - you don't want to loose your cluster.A
>>> kind of 'Best Practice'.
>>>
>>> Best Regards,
>>> Strahil NikolovOn Sep 23, 2019 15:01, TomK <tomkcpr at mdevsys.com> wrote:
>>>> Do I *really* need specific /etc/hosts entries when I have IPA?
>>>>
>>>> [root at mdskvm-p01 ~]# cat /etc/hosts
>>>> 127.0.0.1 localhost localhost.localdomain localhost4
>>>> localhost4.localdomain4
>>>> ::1 localhost localhost.localdomain localhost6
>>>> localhost6.localdomain6
>>>> [root at mdskvm-p01 ~]#
>>>>
>>>> I really shouldn't need too. ( Ref below, everything resolves fine.
>>>> )
>>>>
>>>> Cheers,
>>>> TK
>>>>
>>>>
>>>> On 9/23/2019 1:32 AM, Strahil wrote:
>>>>> Check your /etc/hosts for an entry like:
>>>>> 192.168.0.60 mdskvm-p01.nix.mds.xyz mdskvm-p01
>>>>>
>>>>> Best Regards,
>>>>> Strahil NikolovOn Sep 23, 2019 06:58, TomK <tomkcpr at mdevsys.com>
>>>>> wrote:
>>>>>> Hey All,
>>>>>>
>>>>>> Take the two hosts below as example. One host shows NFS Server on
>>>>>> 192.168.0.60 (FQDN is mdskvm-p01.nix.mds.xyz).
>>>>>>
>>>>>> The other shows mdskvm-p02 (FQDN is mdskvm-p02.nix.mds.xyz).
>>>>>>
>>>>>> Why is there no consistency or correct hostname resolution? Where
>>>>>> does gluster get the hostnames from?
>>>>>>
>>>>>>
>>>>>> [root at mdskvm-p02 glusterfs]# gluster volume status Status of
>>>>>> volume: mdsgv01 Gluster process TCP
>>>>>> Port RDMA Port Online Pid
>>>>>> -------------------------------------------------------------------
>>>>>> ----------- Brick mdskvm-p02.nix.mds.xyz:/mnt/p02-d01/g
>>>>>> lusterv02 49153 0 Y
>>>>>> 17503
>>>>>> Brick mdskvm-p01.nix.mds.xyz:/mnt/p01-d01/g
>>>>>> lusterv01 49153 0 Y
>>>>>> 15044
>>>>>> NFS Server on localhost N/A N/A N
>>>>>> N/A Self-heal Daemon on localhost N/A N/A
>>>>>> Y
>>>>>> 17531
>>>>>> NFS Server on 192.168.0.60 N/A N/A N
>>>>>> N/A Self-heal Daemon on 192.168.0.60 N/A N/A
>>>>>> Y
>>>>>> 15073
>>>>>>
>>>>>> Task Status of Volume mdsgv01
>>>>>> -------------------------------------------------------------------
>>>>>> -----------
>>>>>> There are no active volume tasks
>>>>>>
>>>>>> [root at mdskvm-p02 glusterfs]#
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> [root at mdskvm-p01 ~]# gluster volume status Status of volume:
>>>>>> mdsgv01 Gluster process TCP Port RDMA
>>>>>> Port Online Pid
>>>>>> -------------------------------------------------------------------
>>>>>> ----------- Brick mdskvm-p02.nix.mds.xyz:/mnt/p02-d01/g
>>>>>> lusterv02 49153 0 Y
>>>>>> 17503
>>>>>> Brick mdskvm-p01.nix.mds.xyz:/mnt/p01-d01/g
>>>>>> lusterv01 49153 0 Y
>>>>>> 15044
>>>>>> NFS Server on localhost N/A N/A N
>>>>>> N/A Self-heal Daemon on localhost N/A N/A
>>>>>> Y
>>>>>> 15073
>>>>>> NFS Server on mdskvm-p02 N/A N/A N
>>>>>> N/A Self-heal Daemon on mdskvm-p02 N/A N/A
>>>>>> Y
>>>>>> 17531
>>>>>>
>>>>>> Task Status of Volume mdsgv01
>>>>>> -------------------------------------------------------------------
>>>>>> -----------
>>>>>> There are no active volume tasks
>>>>>>
>>>>>> [root at mdskvm-p01 ~]#
>>>>>>
>>>>>>
>>>>>>
>>>>>> But when verifying everything all seems fine:
>>>>>>
>>>>>>
>>>>>> (1):
>>>>>> [root at mdskvm-p01 glusterfs]# dig -x 192.168.0.39 ;; QUESTION
>>>>>> SECTION:
>>>>>> ;39.0.168.192.in-addr.arpa. IN PTR
>>>>>>
>>>>>> ;; ANSWER SECTION:
>>>>>> 39.0.168.192.in-addr.arpa. 1200 IN PTR
>>>>>> mdskvm-p02.nix.mds.xyz.
>>>>>> [root at mdskvm-p01 glusterfs]# hostname -f mdskvm-p01.nix.mds.xyz
>>>>>> [root at mdskvm-p01 glusterfs]# hostname -s
>>>>>> mdskvm-p01
>>>>>> [root at mdskvm-p01 glusterfs]# hostname mdskvm-p01.nix.mds.xyz
>>>>>> [root at mdskvm-p01 glusterfs]#
>>>>>>
>>>>>>
>>>>>> (2):
>>>>>>
>>>>>> [root at mdskvm-p02 glusterfs]# dig -x 192.168.0.60 ;; QUESTION
>>>>>> SECTION:
>>>>>> ;60.0.168.192.in-addr.arpa. IN PTR
>>>>>>
>>>>>> ;; ANSWER SECTION:
>>>>>> 60.0.168.192.in-addr.arpa. 1200 IN PTR
>>>>>> mdskvm-p01.nix.mds.xyz.
>>>>>>
>>>>>> [root at mdskvm-p02 glusterfs]# hostname -s
>>>>>> mdskvm-p02
>>>>>> [root at mdskvm-p02 glusterfs]# hostname -f mdskvm-p02.nix.mds.xyz
>>>>>> [root at mdskvm-p02 glusterfs]# hostname mdskvm-p02.nix.mds.xyz
>>>>>> [root at mdskvm-p02 glusterfs]#
>>>>>>
>>>>>>
>>>>>> Gluster version used is:
>>>>>>
>>>>>> [root at mdskvm-p01 glusterfs]# rpm -aq|grep -Ei gluster
>>>>>> glusterfs-server-3.12.15-1.el7.x86_64
>>>>>> glusterfs-client-xlators-3.12.15-1.el7.x86_64
>>>>>> glusterfs-rdma-3.12.15-1.el7.x86_64
>>>>>> glusterfs-3.12.15-1.el7.x86_64
>>>>>> glusterfs-events-3.12.15-1.el7.x86_64
>>>>>> libvirt-daemon-driver-storage-gluster-4.5.0-10.el7_6.12.x86_64
>>>>>> glusterfs-libs-3.12.15-1.el7.x86_64
>>>>>> glusterfs-fuse-3.12.15-1.el7.x86_64
>>>>>> glusterfs-geo-replication-3.12.15-1.el7.x86_64
>>>>>> python2-gluster-3.12.15-1.el7.x86_64
>>> ________
>>>
>>> Community Meeting Calendar:
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>>>
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>> ________
>>
>> Community Meeting Calendar:
>>
>> APAC Schedule -
>> Every 2nd and 4th Tuesday at 11:30 AM IST
>> Bridge: https://bluejeans.com/118564314
>>
>> NA/EMEA Schedule -
>> Every 1st and 3rd Tuesday at 01:00 PM EDT
>> Bridge: https://bluejeans.com/118564314
>>
>> Gluster-users mailing list
>> Gluster-users at gluster.org
>> https://lists.gluster.org/mailman/listinfo/gluster-users
>> ________
>>
>> Community Meeting Calendar:
>>
>> APAC Schedule -
>> Every 2nd and 4th Tuesday at 11:30 AM IST
>> Bridge: https://bluejeans.com/118564314
>>
>> NA/EMEA Schedule -
>> Every 1st and 3rd Tuesday at 01:00 PM EDT
>> Bridge: https://bluejeans.com/118564314
>>
>> Gluster-users mailing list
>> Gluster-users at gluster.org
>> https://lists.gluster.org/mailman/listinfo/gluster-users
> ________
>
> Community Meeting Calendar:
>
> APAC Schedule -
> Every 2nd and 4th Tuesday at 11:30 AM IST
> Bridge: https://bluejeans.com/118564314
>
> NA/EMEA Schedule -
> Every 1st and 3rd Tuesday at 01:00 PM EDT
> Bridge: https://bluejeans.com/118564314
>
> Gluster-users mailing list
> Gluster-users at gluster.org
> https://lists.gluster.org/mailman/listinfo/gluster-users
--
Thx,
TK.
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