[Gluster-users] How Does Gluster Failover

[duluxoz]

Hi Guys & Gals,

A Gluster newbie question for sure, but something I just don't "get" (or 
I've missed in the doco, mailing lists, etc):


What happens to a Gluster Client when a Gluster Cluster Node goes 
off-line / fails-over?


How does the Client "know" to use (connect to) another Gluster Node in 
the Gluster Cluster?


Let me elaborate.

I've got four hosts: gfs1, gfs2, gfs3, and client4 sitting on 
192.168.1.1/24, .2, .3, and .4 respectively.


DNS is set up and working correctly.

gfs1, gs2, and gfs3 form a "Gluster Cluster" with a Gluster Volume (gv1) 
replicated across all three nodes. This is all working correctly (ie a 
file (file1) created/modified on gfs1:/gv1 is replicated correctly to 
gfs2:/gv1 and gfs3:/gv1).


client4 has an entry in its /etc/fstab file which reads: "gfs1:gv1  
/data/gv1  glusterfs defaults  0 2". This is also all working correctly 
(ie client4:/data/gv1/file1 is accessible and replicated).


So, (and I haven't tested this yet) what happens to 
client4:/data/gv1/file1 when gfs1 fails (ie is turned off, crashes, etc)?


Does client4 "automatically" switch to using one of the other two 
Gluster Nodes, or do I have something wrong in clients4's /etc/fstab 
file, or an error/mis-configuration somewhere else?


I thought about setting some DNS entries along the lines of:

~~~

glustercluster  IN  A 192.168.0.1

glustercluster  IN  A  192.168.0.2

glustercluster IN  A  192.168.0.3

~~~

and having clients4's /etc/fstab file read: "glustercluster:gv1 
/data/gv1  glusterfs  defaults  0 2", but this is a Round-Robin DNS 
config and I'm not sure how Gluster treats this situation.


So, if people could comment / point me in the correct direction I would 
really appreciate it - thanks.


Dulux-Oz




Community Meeting Calendar:

Schedule -
Every 2nd and 4th Tuesday at 14:30 IST / 09:00 UTC
Bridge: https://meet.google.com/cpu-eiue-hvk
Gluster-users mailing list
Gluster-users@gluster.org
https://lists.gluster.org/mailman/listinfo/gluster-users

Re: [Gluster-users] How Does Gluster Failover

[Karl Kleinpaste]

On 8/31/22 2:55 AM, duluxoz wrote:

what happens to client4:/data/gv1/file1 when gfs1 fails


In part, you can tell the client so explicitly.
mount.glusterfs(8) man page, 2nd instance's syntax:

SYNOPSIS
   mount -t glusterfs [-o ] 
:/[/] 


   mount -t glusterfs [-o ] ,,
,..:/[/] 

   mount -t glusterfs [-o ]  




Community Meeting Calendar:

Schedule -
Every 2nd and 4th Tuesday at 14:30 IST / 09:00 UTC
Bridge: https://meet.google.com/cpu-eiue-hvk
Gluster-users mailing list
Gluster-users@gluster.org
https://lists.gluster.org/mailman/listinfo/gluster-users

Re: [Gluster-users] How Does Gluster Failover

[Joe Julian]

With a replica volume the client connects and writes to all the replicas 
directly. For reads, when a filename is looked up the client checks with 
all the replicas and, if the file is healthy, opens a read connection to 
the first replica to respond (by default).


If a server is shut down, the client receives the tcp messages that 
close the connection. For read operations, it chooses the next server. 
Writes will just continue to the remaining replicas (metadata is stored 
in extended attributes to inform future lookups and the self-healer of 
file health).


If a server crashes (no tcp finalization) the volume will pause for 
ping-timeout seconds (42 by default). Then continue as above. BTW, that 
42 second timeout shouldn't be a big deal. The MTBF should be 
sufficiently far apart that this should still easily get you five or six 
nines.


On 8/30/22 11:55 PM, duluxoz wrote:


Hi Guys & Gals,

A Gluster newbie question for sure, but something I just don't "get" 
(or I've missed in the doco, mailing lists, etc):


What happens to a Gluster Client when a Gluster Cluster Node goes 
off-line / fails-over?


How does the Client "know" to use (connect to) another Gluster Node in 
the Gluster Cluster?


Let me elaborate.

I've got four hosts: gfs1, gfs2, gfs3, and client4 sitting on 
192.168.1.1/24, .2, .3, and .4 respectively.


DNS is set up and working correctly.

gfs1, gs2, and gfs3 form a "Gluster Cluster" with a Gluster Volume 
(gv1) replicated across all three nodes. This is all working correctly 
(ie a file (file1) created/modified on gfs1:/gv1 is replicated 
correctly to gfs2:/gv1 and gfs3:/gv1).


client4 has an entry in its /etc/fstab file which reads: "gfs1:gv1  
/data/gv1 glusterfs  defaults  0 2". This is also all working 
correctly (ie client4:/data/gv1/file1 is accessible and replicated).


So, (and I haven't tested this yet) what happens to 
client4:/data/gv1/file1 when gfs1 fails (ie is turned off, crashes, etc)?


Does client4 "automatically" switch to using one of the other two 
Gluster Nodes, or do I have something wrong in clients4's /etc/fstab 
file, or an error/mis-configuration somewhere else?


I thought about setting some DNS entries along the lines of:

~~~

glustercluster  IN  A 192.168.0.1

glustercluster  IN  A  192.168.0.2

glustercluster IN  A  192.168.0.3

~~~

and having clients4's /etc/fstab file read: "glustercluster:gv1 
/data/gv1  glusterfs  defaults  0 2", but this is a Round-Robin DNS 
config and I'm not sure how Gluster treats this situation.


So, if people could comment / point me in the correct direction I 
would really appreciate it - thanks.


Dulux-Oz






Community Meeting Calendar:

Schedule -
Every 2nd and 4th Tuesday at 14:30 IST / 09:00 UTC
Bridge:https://meet.google.com/cpu-eiue-hvk
Gluster-users mailing list
Gluster-users@gluster.org
https://lists.gluster.org/mailman/listinfo/gluster-users



Community Meeting Calendar:

Schedule -
Every 2nd and 4th Tuesday at 14:30 IST / 09:00 UTC
Bridge: https://meet.google.com/cpu-eiue-hvk
Gluster-users mailing list
Gluster-users@gluster.org
https://lists.gluster.org/mailman/listinfo/gluster-users

Re: [Gluster-users] How Does Gluster Failover

[Matthew J Black]

Hi Joe,

Thanks for getting back to me about this, it was helpful, and I really 
appreciate it.


I am, however, still (slightly) confused - *how* does the client "know" 
the addresses of the other servers in the cluster (for read or write 
purposes), when all the client has is the line in the fstab file: 
"gfs1:gv1  /data/gv1  glusterfs defaults  0 2"? I'm missing something, 
somewhere, in all of this, and I can't work out what that "something" 
is.  :-)


Your help truely is appreciated

Cheers

Dulux-Oz

PEREGRINE IT Signature On 01/09/2022 00:55, Joe Julian wrote:


With a replica volume the client connects and writes to all the 
replicas directly. For reads, when a filename is looked up the client 
checks with all the replicas and, if the file is healthy, opens a read 
connection to the first replica to respond (by default).


If a server is shut down, the client receives the tcp messages that 
close the connection. For read operations, it chooses the next server. 
Writes will just continue to the remaining replicas (metadata is 
stored in extended attributes to inform future lookups and the 
self-healer of file health).


If a server crashes (no tcp finalization) the volume will pause for 
ping-timeout seconds (42 by default). Then continue as above. BTW, 
that 42 second timeout shouldn't be a big deal. The MTBF should be 
sufficiently far apart that this should still easily get you five or 
six nines.


On 8/30/22 11:55 PM, duluxoz wrote:


Hi Guys & Gals,

A Gluster newbie question for sure, but something I just don't "get" 
(or I've missed in the doco, mailing lists, etc):


What happens to a Gluster Client when a Gluster Cluster Node goes 
off-line / fails-over?


How does the Client "know" to use (connect to) another Gluster Node 
in the Gluster Cluster?


Let me elaborate.

I've got four hosts: gfs1, gfs2, gfs3, and client4 sitting on 
192.168.1.1/24, .2, .3, and .4 respectively.


DNS is set up and working correctly.

gfs1, gs2, and gfs3 form a "Gluster Cluster" with a Gluster Volume 
(gv1) replicated across all three nodes. This is all working 
correctly (ie a file (file1) created/modified on gfs1:/gv1 is 
replicated correctly to gfs2:/gv1 and gfs3:/gv1).


client4 has an entry in its /etc/fstab file which reads: "gfs1:gv1  
/data/gv1 glusterfs  defaults  0 2". This is also all working 
correctly (ie client4:/data/gv1/file1 is accessible and replicated).


So, (and I haven't tested this yet) what happens to 
client4:/data/gv1/file1 when gfs1 fails (ie is turned off, crashes, etc)?


Does client4 "automatically" switch to using one of the other two 
Gluster Nodes, or do I have something wrong in clients4's /etc/fstab 
file, or an error/mis-configuration somewhere else?


I thought about setting some DNS entries along the lines of:

~~~

glustercluster  IN  A 192.168.0.1

glustercluster  IN  A  192.168.0.2

glustercluster IN  A  192.168.0.3

~~~

and having clients4's /etc/fstab file read: "glustercluster:gv1  
/data/gv1  glusterfs  defaults  0 2", but this is a Round-Robin DNS 
config and I'm not sure how Gluster treats this situation.


So, if people could comment / point me in the correct direction I 
would really appreciate it - thanks.


Dulux-Oz






Community Meeting Calendar:

Schedule -
Every 2nd and 4th Tuesday at 14:30 IST / 09:00 UTC
Bridge:https://meet.google.com/cpu-eiue-hvk
Gluster-users mailing list
Gluster-users@gluster.org
https://lists.gluster.org/mailman/listinfo/gluster-users


--
This email has been checked for viruses by Avast antivirus software.
www.avast.com



Community Meeting Calendar:

Schedule -
Every 2nd and 4th Tuesday at 14:30 IST / 09:00 UTC
Bridge: https://meet.google.com/cpu-eiue-hvk
Gluster-users mailing list
Gluster-users@gluster.org
https://lists.gluster.org/mailman/listinfo/gluster-users

Re: [Gluster-users] How Does Gluster Failover

[Joe Julian]

You know when you do a `gluster volume info` and you get the whole 
volume definition, the client graph is built from the same info. In 
fact, if you look in /var/lib/glusterd/vols/$volume_name you'll find 
some ".vol" files. `$volume_name.tcp-fuse.vol` is the configuration that 
the clients receive from whichever server they initially connect to. 
You'll notice that file has multiple "type/client" sections, each 
establishing a tcp connection to a server.


Sidenote: You can also see in that file, how the microkernels are used 
to build all the logic that forms the volume, which is kinda cool. Back 
when I first started using gluster, there was no glusterd and you have 
to build those .vol files by hand.


On 8/31/22 8:04 AM, Matthew J Black wrote:


Hi Joe,

Thanks for getting back to me about this, it was helpful, and I really 
appreciate it.


I am, however, still (slightly) confused - *how* does the client 
"know" the addresses of the other servers in the cluster (for read or 
write purposes), when all the client has is the line in the fstab 
file: "gfs1:gv1  /data/gv1  glusterfs defaults  0 2"? I'm missing 
something, somewhere, in all of this, and I can't work out what that 
"something" is.  :-)


Your help truely is appreciated

Cheers

Dulux-Oz

PEREGRINE IT Signature On 01/09/2022 00:55, Joe Julian wrote:


With a replica volume the client connects and writes to all the 
replicas directly. For reads, when a filename is looked up the client 
checks with all the replicas and, if the file is healthy, opens a 
read connection to the first replica to respond (by default).


If a server is shut down, the client receives the tcp messages that 
close the connection. For read operations, it chooses the next 
server. Writes will just continue to the remaining replicas (metadata 
is stored in extended attributes to inform future lookups and the 
self-healer of file health).


If a server crashes (no tcp finalization) the volume will pause for 
ping-timeout seconds (42 by default). Then continue as above. BTW, 
that 42 second timeout shouldn't be a big deal. The MTBF should be 
sufficiently far apart that this should still easily get you five or 
six nines.


On 8/30/22 11:55 PM, duluxoz wrote:


Hi Guys & Gals,

A Gluster newbie question for sure, but something I just don't "get" 
(or I've missed in the doco, mailing lists, etc):


What happens to a Gluster Client when a Gluster Cluster Node goes 
off-line / fails-over?


How does the Client "know" to use (connect to) another Gluster Node 
in the Gluster Cluster?


Let me elaborate.

I've got four hosts: gfs1, gfs2, gfs3, and client4 sitting on 
192.168.1.1/24, .2, .3, and .4 respectively.


DNS is set up and working correctly.

gfs1, gs2, and gfs3 form a "Gluster Cluster" with a Gluster Volume 
(gv1) replicated across all three nodes. This is all working 
correctly (ie a file (file1) created/modified on gfs1:/gv1 is 
replicated correctly to gfs2:/gv1 and gfs3:/gv1).


client4 has an entry in its /etc/fstab file which reads: "gfs1:gv1  
/data/gv1 glusterfs  defaults  0 2". This is also all working 
correctly (ie client4:/data/gv1/file1 is accessible and replicated).


So, (and I haven't tested this yet) what happens to 
client4:/data/gv1/file1 when gfs1 fails (ie is turned off, crashes, 
etc)?


Does client4 "automatically" switch to using one of the other two 
Gluster Nodes, or do I have something wrong in clients4's /etc/fstab 
file, or an error/mis-configuration somewhere else?


I thought about setting some DNS entries along the lines of:

~~~

glustercluster  IN  A 192.168.0.1

glustercluster  IN  A  192.168.0.2

glustercluster IN  A  192.168.0.3

~~~

and having clients4's /etc/fstab file read: "glustercluster:gv1  
/data/gv1  glusterfs  defaults  0 2", but this is a Round-Robin DNS 
config and I'm not sure how Gluster treats this situation.


So, if people could comment / point me in the correct direction I 
would really appreciate it - thanks.


Dulux-Oz






Community Meeting Calendar:

Schedule -
Every 2nd and 4th Tuesday at 14:30 IST / 09:00 UTC
Bridge:https://meet.google.com/cpu-eiue-hvk
Gluster-users mailing list
Gluster-users@gluster.org
https://lists.gluster.org/mailman/listinfo/gluster-users


width= 
 
	Virus-free.www.avast.com 
 



<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>



Community Meeting Calendar:

Schedule -
Every 2nd and 4th Tuesday at 14:30 IST / 09:00 UTC
Bridge: https://meet.google.com/cpu-eiue-hvk
Gluster-users mailing list
Gluster-users@gluster.org
https://lists.gluster.org/mailman/listinfo/gluster-users

Re: [Gluster-users] How Does Gluster Failover

[Matthew J Black]

Ah, it all now falls into place: I was unaware that the client receives 
that file upon initial contact with the cluster, and thus has that 
information at hand independently of the cluster nodes.


Thank you for taking the time to educate a poor newbie - it is very much 
appreciated.


Cheers

Dulux-Oz

PEREGRINE IT Signature On 01/09/2022 01:16, Joe Julian wrote:


You know when you do a `gluster volume info` and you get the whole 
volume definition, the client graph is built from the same info. In 
fact, if you look in /var/lib/glusterd/vols/$volume_name you'll find 
some ".vol" files. `$volume_name.tcp-fuse.vol` is the configuration 
that the clients receive from whichever server they initially connect 
to. You'll notice that file has multiple "type/client" sections, each 
establishing a tcp connection to a server.


Sidenote: You can also see in that file, how the microkernels are used 
to build all the logic that forms the volume, which is kinda cool. 
Back when I first started using gluster, there was no glusterd and you 
have to build those .vol files by hand.


On 8/31/22 8:04 AM, Matthew J Black wrote:


Hi Joe,

Thanks for getting back to me about this, it was helpful, and I 
really appreciate it.


I am, however, still (slightly) confused - *how* does the client 
"know" the addresses of the other servers in the cluster (for read or 
write purposes), when all the client has is the line in the fstab 
file: "gfs1:gv1 /data/gv1  glusterfs  defaults  0 2"? I'm missing 
something, somewhere, in all of this, and I can't work out what that 
"something" is.  :-)


Your help truely is appreciated

Cheers

Dulux-Oz

PEREGRINE IT Signature On 01/09/2022 00:55, Joe Julian wrote:


With a replica volume the client connects and writes to all the 
replicas directly. For reads, when a filename is looked up the 
client checks with all the replicas and, if the file is healthy, 
opens a read connection to the first replica to respond (by default).


If a server is shut down, the client receives the tcp messages that 
close the connection. For read operations, it chooses the next 
server. Writes will just continue to the remaining replicas 
(metadata is stored in extended attributes to inform future lookups 
and the self-healer of file health).


If a server crashes (no tcp finalization) the volume will pause for 
ping-timeout seconds (42 by default). Then continue as above. BTW, 
that 42 second timeout shouldn't be a big deal. The MTBF should be 
sufficiently far apart that this should still easily get you five or 
six nines.


On 8/30/22 11:55 PM, duluxoz wrote:


Hi Guys & Gals,

A Gluster newbie question for sure, but something I just don't 
"get" (or I've missed in the doco, mailing lists, etc):


What happens to a Gluster Client when a Gluster Cluster Node goes 
off-line / fails-over?


How does the Client "know" to use (connect to) another Gluster Node 
in the Gluster Cluster?


Let me elaborate.

I've got four hosts: gfs1, gfs2, gfs3, and client4 sitting on 
192.168.1.1/24, .2, .3, and .4 respectively.


DNS is set up and working correctly.

gfs1, gs2, and gfs3 form a "Gluster Cluster" with a Gluster Volume 
(gv1) replicated across all three nodes. This is all working 
correctly (ie a file (file1) created/modified on gfs1:/gv1 is 
replicated correctly to gfs2:/gv1 and gfs3:/gv1).


client4 has an entry in its /etc/fstab file which reads: "gfs1:gv1  
/data/gv1 glusterfs  defaults  0 2". This is also all working 
correctly (ie client4:/data/gv1/file1 is accessible and replicated).


So, (and I haven't tested this yet) what happens to 
client4:/data/gv1/file1 when gfs1 fails (ie is turned off, crashes, 
etc)?


Does client4 "automatically" switch to using one of the other two 
Gluster Nodes, or do I have something wrong in clients4's 
/etc/fstab file, or an error/mis-configuration somewhere else?


I thought about setting some DNS entries along the lines of:

~~~

glustercluster  IN  A 192.168.0.1

glustercluster  IN  A  192.168.0.2

glustercluster IN  A  192.168.0.3

~~~

and having clients4's /etc/fstab file read: "glustercluster:gv1  
/data/gv1  glusterfs  defaults 0 2", but this is a Round-Robin DNS 
config and I'm not sure how Gluster treats this situation.


So, if people could comment / point me in the correct direction I 
would really appreciate it - thanks.


Dulux-Oz






Community Meeting Calendar:

Schedule -
Every 2nd and 4th Tuesday at 14:30 IST / 09:00 UTC
Bridge:https://meet.google.com/cpu-eiue-hvk
Gluster-users mailing list
Gluster-users@gluster.org
https://lists.gluster.org/mailman/listinfo/gluster-users


width= 
 
	Virus-free.www.avast.com 
 



<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>


--
This email has been checked for viruses by Avast antivirus software.
ww

Re: [Gluster-users] How Does Gluster Failover

[Péter Károly JUHÁSZ]

You can also add the mount option: backupvolfile-server to let the client
know the other nodes.

Matthew J Black  于 2022年8月31日周三 17:21写道：

> Ah, it all now falls into place: I was unaware that the client receives
> that file upon initial contact with the cluster, and thus has that
> information at hand independently of the cluster nodes.
>
> Thank you for taking the time to educate a poor newbie - it is very much
> appreciated.
>
> Cheers
>
> Dulux-Oz
> On 01/09/2022 01:16, Joe Julian wrote:
>
> You know when you do a `gluster volume info` and you get the whole volume
> definition, the client graph is built from the same info. In fact, if you
> look in /var/lib/glusterd/vols/$volume_name you'll find some ".vol" files.
> `$volume_name.tcp-fuse.vol` is the configuration that the clients receive
> from whichever server they initially connect to. You'll notice that file
> has multiple "type/client" sections, each establishing a tcp connection to
> a server.
>
> Sidenote: You can also see in that file, how the microkernels are used to
> build all the logic that forms the volume, which is kinda cool. Back when I
> first started using gluster, there was no glusterd and you have to build
> those .vol files by hand.
> On 8/31/22 8:04 AM, Matthew J Black wrote:
>
> Hi Joe,
>
> Thanks for getting back to me about this, it was helpful, and I really
> appreciate it.
>
> I am, however, still (slightly) confused - *how* does the client "know"
> the addresses of the other servers in the cluster (for read or write
> purposes), when all the client has is the line in the fstab file: "gfs1:gv1
> /data/gv1  glusterfs  defaults  0 2"? I'm missing something, somewhere,
> in all of this, and I can't work out what that "something" is.  :-)
>
> Your help truely is appreciated
>
> Cheers
>
> Dulux-Oz
> On 01/09/2022 00:55, Joe Julian wrote:
>
> With a replica volume the client connects and writes to all the replicas
> directly. For reads, when a filename is looked up the client checks with
> all the replicas and, if the file is healthy, opens a read connection to
> the first replica to respond (by default).
>
> If a server is shut down, the client receives the tcp messages that close
> the connection. For read operations, it chooses the next server. Writes
> will just continue to the remaining replicas (metadata is stored in
> extended attributes to inform future lookups and the self-healer of file
> health).
>
> If a server crashes (no tcp finalization) the volume will pause for
> ping-timeout seconds (42 by default). Then continue as above. BTW, that 42
> second timeout shouldn't be a big deal. The MTBF should be sufficiently far
> apart that this should still easily get you five or six nines.
> On 8/30/22 11:55 PM, duluxoz wrote:
>
> Hi Guys & Gals,
>
> A Gluster newbie question for sure, but something I just don't "get" (or
> I've missed in the doco, mailing lists, etc):
>
> What happens to a Gluster Client when a Gluster Cluster Node goes off-line
> / fails-over?
>
> How does the Client "know" to use (connect to) another Gluster Node in the
> Gluster Cluster?
>
> Let me elaborate.
>
> I've got four hosts: gfs1, gfs2, gfs3, and client4 sitting on
> 192.168.1.1/24, .2, .3, and .4 respectively.
>
> DNS is set up and working correctly.
>
> gfs1, gs2, and gfs3 form a "Gluster Cluster" with a Gluster Volume (gv1)
> replicated across all three nodes. This is all working correctly (ie a file
> (file1) created/modified on gfs1:/gv1 is replicated correctly to gfs2:/gv1
> and gfs3:/gv1).
>
> client4 has an entry in its /etc/fstab file which reads: "gfs1:gv1
> /data/gv1  glusterfs  defaults  0 2". This is also all working correctly
> (ie client4:/data/gv1/file1 is accessible and replicated).
>
> So, (and I haven't tested this yet) what happens to client4:/data/gv1/file1
> when gfs1 fails (ie is turned off, crashes, etc)?
>
> Does client4 "automatically" switch to using one of the other two Gluster
> Nodes, or do I have something wrong in clients4's /etc/fstab file, or an
> error/mis-configuration somewhere else?
>
> I thought about setting some DNS entries along the lines of:
>
> ~~~
>
> glustercluster  IN  A  192.168.0.1
>
> glustercluster  IN  A  192.168.0.2
>
> glustercluster  IN  A  192.168.0.3
>
> ~~~
>
> and having clients4's /etc/fstab file read: "glustercluster:gv1
> /data/gv1  glusterfs  defaults  0 2", but this is a Round-Robin DNS
> config and I'm not sure how Gluster treats this situation.
>
> So, if people could comment / point me in the correct direction I would
> really appreciate it - thanks.
>
> Dulux-Oz
>
> 
>
>
>
> Community Meeting Calendar:
>
> Schedule -
> Every 2nd and 4th Tuesday at 14:30 IST / 09:00 UTC
> Bridge: https://meet.google.com/cpu-eiue-hvk
> Gluster-users mailing 
> listGluster-users@gluster.orghttps://lists.gluster.org/mailman/listinfo/gluster-users
>
>
> [image: width=]
> 
> Virus-fre

Re: [Gluster-users] How Does Gluster Failover

[Joe Julian]

Kind-of. That just tells the client what other nodes it can use to 
retrieve that volume configuration. It's only used during that initial 
fetch.


On 8/31/22 8:26 AM, Péter Károly JUHÁSZ wrote:
You can also add the mount option: backupvolfile-server to let the 
client know the other nodes.


Matthew J Black  于 2022年8月31日周三 17:21写道：

Ah, it all now falls into place: I was unaware that the client
receives that file upon initial contact with the cluster, and thus
has that information at hand independently of the cluster nodes.

Thank you for taking the time to educate a poor newbie - it is
very much appreciated.

Cheers

Dulux-Oz

On 01/09/2022 01:16, Joe Julian wrote:


You know when you do a `gluster volume info` and you get the
whole volume definition, the client graph is built from the same
info. In fact, if you look in /var/lib/glusterd/vols/$volume_name
you'll find some ".vol" files. `$volume_name.tcp-fuse.vol` is the
configuration that the clients receive from whichever server they
initially connect to. You'll notice that file has multiple
"type/client" sections, each establishing a tcp connection to a
server.

Sidenote: You can also see in that file, how the microkernels are
used to build all the logic that forms the volume, which is kinda
cool. Back when I first started using gluster, there was no
glusterd and you have to build those .vol files by hand.

On 8/31/22 8:04 AM, Matthew J Black wrote:


Hi Joe,

Thanks for getting back to me about this, it was helpful, and I
really appreciate it.

I am, however, still (slightly) confused - *how* does the client
"know" the addresses of the other servers in the cluster (for
read or write purposes), when all the client has is the line in
the fstab file: "gfs1:gv1  /data/gv1  glusterfs defaults  0 2"?
I'm missing something, somewhere, in all of this, and I can't
work out what that "something" is.  :-)

Your help truely is appreciated

Cheers

Dulux-Oz

On 01/09/2022 00:55, Joe Julian wrote:


With a replica volume the client connects and writes to all the
replicas directly. For reads, when a filename is looked up the
client checks with all the replicas and, if the file is
healthy, opens a read connection to the first replica to
respond (by default).

If a server is shut down, the client receives the tcp messages
that close the connection. For read operations, it chooses the
next server. Writes will just continue to the remaining
replicas (metadata is stored in extended attributes to inform
future lookups and the self-healer of file health).

If a server crashes (no tcp finalization) the volume will pause
for ping-timeout seconds (42 by default). Then continue as
above. BTW, that 42 second timeout shouldn't be a big deal. The
MTBF should be sufficiently far apart that this should still
easily get you five or six nines.

On 8/30/22 11:55 PM, duluxoz wrote:


Hi Guys & Gals,

A Gluster newbie question for sure, but something I just don't
"get" (or I've missed in the doco, mailing lists, etc):

What happens to a Gluster Client when a Gluster Cluster Node
goes off-line / fails-over?

How does the Client "know" to use (connect to) another Gluster
Node in the Gluster Cluster?

Let me elaborate.

I've got four hosts: gfs1, gfs2, gfs3, and client4 sitting on
192.168.1.1/24 , .2, .3, and .4
respectively.

DNS is set up and working correctly.

gfs1, gs2, and gfs3 form a "Gluster Cluster" with a Gluster
Volume (gv1) replicated across all three nodes. This is all
working correctly (ie a file (file1) created/modified on
gfs1:/gv1 is replicated correctly to gfs2:/gv1 and gfs3:/gv1).

client4 has an entry in its /etc/fstab file which reads:
"gfs1:gv1  /data/gv1  glusterfs  defaults  0 2". This is also
all working correctly (ie client4:/data/gv1/file1 is
accessible and replicated).

So, (and I haven't tested this yet) what happens to
client4:/data/gv1/file1 when gfs1 fails (ie is turned off,
crashes, etc)?

Does client4 "automatically" switch to using one of the other
two Gluster Nodes, or do I have something wrong in clients4's
/etc/fstab file, or an error/mis-configuration somewhere else?

I thought about setting some DNS entries along the lines of:

~~~

glustercluster IN  A  192.168.0.1

glustercluster  IN  A 192.168.0.2

glustercluster  IN  A 192.168.0.3

~~~

and having clients4's /etc/fstab file read:
"glustercluster:gv1  /data/gv1  glusterfs defaults  0 2", but
this is a Round-Robin DNS config and I'm not sure how Gluster
treats this situation.

So, if people could comment / point me in the correct
direction I would really appreciate it - thanks.

Dulux-Oz






Community Meetin

Re: [Gluster-users] How Does Gluster Failover

[Joe Julian]

By that same token, you can also use a hostname with multiple A records 
and glusterd will use those for failover to retrieve the vol file.


On 8/31/22 8:32 AM, Joe Julian wrote:


Kind-of. That just tells the client what other nodes it can use to 
retrieve that volume configuration. It's only used during that initial 
fetch.


On 8/31/22 8:26 AM, Péter Károly JUHÁSZ wrote:
You can also add the mount option: backupvolfile-server to let the 
client know the other nodes.


Matthew J Black  于 2022年8月31日周三 17:21写道：

Ah, it all now falls into place: I was unaware that the client
receives that file upon initial contact with the cluster, and
thus has that information at hand independently of the cluster nodes.

Thank you for taking the time to educate a poor newbie - it is
very much appreciated.

Cheers

Dulux-Oz

On 01/09/2022 01:16, Joe Julian wrote:


You know when you do a `gluster volume info` and you get the
whole volume definition, the client graph is built from the same
info. In fact, if you look in
/var/lib/glusterd/vols/$volume_name you'll find some ".vol"
files. `$volume_name.tcp-fuse.vol` is the configuration that the
clients receive from whichever server they initially connect to.
You'll notice that file has multiple "type/client" sections,
each establishing a tcp connection to a server.

Sidenote: You can also see in that file, how the microkernels
are used to build all the logic that forms the volume, which is
kinda cool. Back when I first started using gluster, there was
no glusterd and you have to build those .vol files by hand.

On 8/31/22 8:04 AM, Matthew J Black wrote:


Hi Joe,

Thanks for getting back to me about this, it was helpful, and I
really appreciate it.

I am, however, still (slightly) confused - *how* does the
client "know" the addresses of the other servers in the cluster
(for read or write purposes), when all the client has is the
line in the fstab file: "gfs1:gv1  /data/gv1  glusterfs
defaults  0 2"? I'm missing something, somewhere, in all of
this, and I can't work out what that "something" is.  :-)

Your help truely is appreciated

Cheers

Dulux-Oz

On 01/09/2022 00:55, Joe Julian wrote:


With a replica volume the client connects and writes to all
the replicas directly. For reads, when a filename is looked up
the client checks with all the replicas and, if the file is
healthy, opens a read connection to the first replica to
respond (by default).

If a server is shut down, the client receives the tcp messages
that close the connection. For read operations, it chooses the
next server. Writes will just continue to the remaining
replicas (metadata is stored in extended attributes to inform
future lookups and the self-healer of file health).

If a server crashes (no tcp finalization) the volume will
pause for ping-timeout seconds (42 by default). Then continue
as above. BTW, that 42 second timeout shouldn't be a big deal.
The MTBF should be sufficiently far apart that this should
still easily get you five or six nines.

On 8/30/22 11:55 PM, duluxoz wrote:


Hi Guys & Gals,

A Gluster newbie question for sure, but something I just
don't "get" (or I've missed in the doco, mailing lists, etc):

What happens to a Gluster Client when a Gluster Cluster Node
goes off-line / fails-over?

How does the Client "know" to use (connect to) another
Gluster Node in the Gluster Cluster?

Let me elaborate.

I've got four hosts: gfs1, gfs2, gfs3, and client4 sitting on
192.168.1.1/24 , .2, .3, and .4
respectively.

DNS is set up and working correctly.

gfs1, gs2, and gfs3 form a "Gluster Cluster" with a Gluster
Volume (gv1) replicated across all three nodes. This is all
working correctly (ie a file (file1) created/modified on
gfs1:/gv1 is replicated correctly to gfs2:/gv1 and gfs3:/gv1).

client4 has an entry in its /etc/fstab file which reads:
"gfs1:gv1  /data/gv1  glusterfs  defaults  0 2". This is also
all working correctly (ie client4:/data/gv1/file1 is
accessible and replicated).

So, (and I haven't tested this yet) what happens to
client4:/data/gv1/file1 when gfs1 fails (ie is turned off,
crashes, etc)?

Does client4 "automatically" switch to using one of the other
two Gluster Nodes, or do I have something wrong in clients4's
/etc/fstab file, or an error/mis-configuration somewhere else?

I thought about setting some DNS entries along the lines of:

~~~

glustercluster IN  A  192.168.0.1

glustercluster IN  A  192.168.0.2

glustercluster  IN  A 192.168.0.3

~~~

and having clients4's /etc/fstab file read:
"glustercluster:gv1  /data/gv1  glusterfs defaults  0 2", but
this is a Round-Robin DNS config and I'm not sure how Gluster
treat