Secondary HANA server becomes unavailable

Simulated Failures

Instance failures. The secondary HANA instance is crashed or not anymore reachable through the network
Availability zone failure.

Components getting tested

EC2 stoneith agent
HANA agent
Overlay IP agent
Optional: Route 53 agent if it is configured

Approach

Have a correctly working HANA DB cluster
Shutdown eth0 on the secondary server to isolate the server
The cluster will shutdown the the secondary node
The cluster will keep the primary node running without replication
The cluster will not restart the failed node

Intial Configuration

Check whether the overlay IP address gets hosted on the interface eth0 on the first node:

hana01:/var/log # ip address list eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9000 qdisc mq state UP group default qlen 1000
    link/ether 02:ca:c9:ca:a6:52 brd ff:ff:ff:ff:ff:ff
    inet 10.0.1.115/24 brd 10.0.1.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet 192.168.10.21/32 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::ca:c9ff:feca:a652/64 scope link 
       valid_lft forever preferred_lft forever

Check the cluster status as super user with the command crm status:

hana01:/var/log # crm status
Stack: corosync
Current DC: hana02 (version 1.1.15-21.1-e174ec8) - partition with quorum
Last updated: Tue Sep 11 12:37:53 2018
Last change: Tue Sep 11 12:37:53 2018 by root via crm_attribute on hana012 nodes configured
6 resources configured
Online: [ hana01 hana02 ]
Full list of resources:
res_AWS_STONITH	(stonith:external/ec2):	Started hana01
 res_AWS_IP	(ocf::heartbeat:aws-vpc-move-ip):	Started hana01
 Clone Set: cln_SAPHanaTopology_HDB_HDB00 [rsc_SAPHanaTopology_HDB_HDB00]
     Started: [ hana01 hana02 ]
 Master/Slave Set: msl_SAPHana_HDB_HDB00 [rsc_SAPHana_HDB_HDB00]
     Masters: [ hana01 ]
     Slaves: [ hana02 ]

Status of HANA replication:

hana01:/home/ec2-user # SAPHanaSR-showAttr

Global cib-time
--------------------------------
global Wed Sep 19 14:23:11 2018

Hosts clone_state lpa_hdb_lpt node_state op_mode remoteHost roles score site srmode sync_state version vhost
-----------------------------------------------------------------------------------------------------------------------------------------------------------
hana01 PROMOTED 1537366980 online logreplay hana02 4:P:master1:master:worker:master 150 WDF sync PRIM 2.00.030.00.1522209842 hana01
hana02 DEMOTED 30 online logreplay hana01 4:S:master1:master:worker:master 100 ROT sync SOK 2.00.030.00.1522209842 hana02

The AWS console shows that both nodes are running:

Screenshot two running nodes

Damage the Instance

There are two ways to "damage" an instance

Corrupt Kernel

Become super user on the secondary HANA node.

Issue the command:

echo 'b' > /proc/sysrq-trigger

Isolate secondary Instance

Become super user on the secondary HANA node.

Issue the command:

$ ifdown eth0

The current session will now hang. The system will not be able to communicate with the network anymore.

SUSE has a recommendation to do the isolation with firewalls and IP tables.

Monitor Fail Over

Expect the following in a correct working cluster:

The first node will fence the second node. This means it will force a shutdown through AWS CLI commands
The second node will be stopped
The first node will remain the master node of the HANA database.
There is no more replication!

Monitor progress from the master node!

The first node gets reported being offline:

hana01:/home/ec2-user # SAPHanaSR-showAttr
Global cib-time
--------------------------------
global Wed Sep 19 14:24:13 2018

Hosts clone_state lpa_hdb_lpt node_state op_mode remoteHost roles score site srmode sync_state version vhost
-----------------------------------------------------------------------------------------------------------------------------------------------------------
hana01 PROMOTED 1537367044 online logreplay hana02 4:P:master1:master:worker:master 150 WDF sync PRIM 2.00.030.00.1522209842 hana01
hana02 DEMOTED 30 offline logreplay hana01 4:S:master1:master:worker:master 100 ROT sync SOK 2.00.030.00.1522209842 hana02

The cluster will figure out that the secondary node is in an unclean state

hana01:/home/ec2-user # crm_mon -1rfn
Stack: corosync
Current DC: hana01 (version 1.1.15-21.1-e174ec8) - partition with quorum
Last updated: Wed Sep 19 14:24:26 2018
Last change: Wed Sep 19 14:24:13 2018 by root via crm_attribute on hana01

2 nodes configured
6 resources configured
Node hana01: online
rsc_SAPHana_HDB_HDB00	(ocf::suse:SAPHana):	Master
res_AWS_STONITH	(stonith:external/ec2):	Started
rsc_SAPHanaTopology_HDB_HDB00	(ocf::suse:SAPHanaTopology):	Started
res_AWS_IP	(ocf::heartbeat:aws-vpc-move-ip):	Started
Node hana02: UNCLEAN (offline)
res_AWS_STONITH	(stonith:external/ec2):	Started
rsc_SAPHanaTopology_HDB_HDB00	(ocf::suse:SAPHanaTopology):	Started
rsc_SAPHana_HDB_HDB00	(ocf::suse:SAPHana):	Slave
Inactive resources:
Migration Summary:
* Node hana01:

The AWS console will now show that the master node has been fencing the secondary node node. It gets shut down:

Screenshot node gets shut down

The master node will wait until the secondary node is shut down. The AWS console will look like:

Secondary node being shut down

The cluster will now reconfigure it HANA configuration. The cluster knows that the node is offline and replication has been stopped:

hana01:/home/ec2-user # SAPHanaSR-showAttr
Global cib-time
--------------------------------
global Wed Sep 19 14:24:13 2018

Hosts clone_state lpa_hdb_lpt node_state op_mode remoteHost roles score site srmode sync_state version vhost
-----------------------------------------------------------------------------------------------------------------------------------------------------------
hana01 PROMOTED 1537367044 online logreplay hana02 4:P:master1:master:worker:master 150 WDF sync PRIM 2.00.030.00.1522209842 hana01
hana02 30 offline logreplay hana01 ROT sync hana02

The cluster status is the following:

hana01:/home/ec2-user # crm_mon -1rfn
Stack: corosync
Current DC: hana01 (version 1.1.15-21.1-e174ec8) - partition with quorum
Last updated: Wed Sep 19 14:27:05 2018
Last change: Wed Sep 19 14:24:13 2018 by root via crm_attribute on hana01

2 nodes configured
6 resources configured
Node hana01: online
rsc_SAPHana_HDB_HDB00	(ocf::suse:SAPHana):	Master
res_AWS_STONITH	(stonith:external/ec2):	Started
rsc_SAPHanaTopology_HDB_HDB00	(ocf::suse:SAPHanaTopology):	Started
res_AWS_IP	(ocf::heartbeat:aws-vpc-move-ip):	Started
Node hana02: OFFLINE
Inactive resources:
Clone Set: cln_SAPHanaTopology_HDB_HDB00 [rsc_SAPHanaTopology_HDB_HDB00]
     Started: [ hana01 ]
     Stopped: [ hana02 ]
 Master/Slave Set: msl_SAPHana_HDB_HDB00 [rsc_SAPHana_HDB_HDB00]
     Masters: [ hana01 ]
     Stopped: [ hana02 ]
Migration Summary:
* Node hana01:
   res_AWS_STONITH: migration-threshold=5000 fail-count=1 last-failure='Wed Sep 19 14:26:17 2018'
Failed Actions:
* res_AWS_STONITH_monitor_120000 on hana01 'unknown error' (1): call=-1, status=Timed Out, exitreason='none',
    last-rc-change='Wed Sep 19 14:26:17 2018', queued=0ms, exec=0ms

Check whether the overlay IP address gets hosted on the eth0 interface of the master node. Example:

hana01:/home/ec2-user # ip address list eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9000 qdisc mq state UP group default qlen 1000
    link/ether 02:ca:c9:ca:a6:52 brd ff:ff:ff:ff:ff:ff
    inet 10.0.1.115/24 brd 10.0.1.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet 192.168.10.21/32 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::ca:c9ff:feca:a652/64 scope link
       valid_lft forever preferred_lft forever

Recovering the Cluster

Restart your stopped node.
Check whether the cluster services get started
Check whether the first node becomes a replicating server

See:

hana01:/home/ec2-user # SAPHanaSR-showAttr
Global cib-time
--------------------------------
global Wed Sep 19 14:59:15 2018

Hosts clone_state lpa_hdb_lpt node_state op_mode remoteHost roles score site srmode sync_state version vhost
-----------------------------------------------------------------------------------------------------------------------------------------------------------
hana01 PROMOTED 1537369155 online logreplay hana02 4:P:master1:master:worker:master 150 WDF sync PRIM 2.00.030.00.1522209842 hana01
hana02 DEMOTED 30 online logreplay hana01 4:S:master1:master:worker:master 100 ROT sync SOK 2.00.030.00.1522209842 hana02

Stefan Schneider Wed, 09/19/2018 - 16:12

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