I have an Elasticsearch cluster in a VPN.
How can my Spring Boot application access the cluster securely if it is located on a separate server outside of the VPN and how can I configure it in the Spring boot configuration (application.yml/application.properties)?
I also want the application to connect to the cluster i an way so that if i have e.g. 2 Master eligible nodes and one fails, the connection remains intact.
if you have only 2 master eligble nodes, you are at risk of the "split brain problem". there is a easy formula for the calculation of the required number of master nodes:
M = 2F +1 ( m=master node count, f=number of master nodes possible to fail at same time)
in your application define all master nodes as target for the elasticsearch client. The client will handle the failover. see elasticsearc client documentation or https://qbox.io/blog/rest-calls-made-easy-part-2-sniffing-elasticsearch for a example
the vpn should not be handled by your application. the infrastructure (server, firewall) is the right place to address it. try to develop your application environment agnostic. this will make your app easier to develop, maintain and make it more robust to infrastructure changes
Related
I have two servers in a HA mode. I'd like to know if is it possible to deploy an application on the slave server? If yes, how to configure it in jgroups? I need to run a specific program that access the master database, but I would not like to run on master serve to avoid overhead on it.
JGroups itself does not know much about WildFly and the deployments, it only creates a communication channel between nodes. I don't know where you get the notion of master/slave, but JGroups always has single* node marked as coordinator. You can check the membership through Channel.getView().
However, you still need to deploy the app on both nodes and just make it inactive if this is not its target node.
*) If there's no split-brain partition, or similar rare/temporal issues
I have cluster of 3 Mesos slaves, where I have two applications: “redis” and “memcached”. Where redis depends on memcached and the requirement is both of the applications/services should start on same node instead of different slave nodes.
So I have created the application group and added the dependency properly in the JSON file. After launching the JSON file via “v2/groups” REST API, I observe that sometime both application group will start on same node but sometimes it will start on different slaves which breaks our requirement.
So intent/requirement is; if any application fails to start on a slave both the application should failover to other slave node. Also can I configure the JSON file to tell Marathon to start the application group on slave-1 (specific slave first) if it is available else start it on other slave in a cluster. Due to some reason if this application group will start on other slave can Marathon relaunch the application group to slave-1 if it is available to serve the request.
Thanks in advance for help.
Edit/Update (2):
Mesos, Marathon, and DC/OS support for PODs is available now:
DC/OS: https://dcos.io/docs/1.9/usage/pods/using-pods/
Mesos: https://github.com/apache/mesos/blob/master/docs/nested-container-and-task-group.md
Marathon: https://github.com/mesosphere/marathon/blob/master/docs/docs/pods.md
I assume you are talking about marathon apps.
Marathon application groups don't have any semantics concerning co-location on the same node and the same is the case for dependencies.
You seem to be looking for a Kubernetes like Pod abstraction in marathon, which is on the roadmap but not yet available (see update above :-)).
Hope this helps!
I think this should be possible (as a workaround) if you specify the correct app contraints within the group's JSON.
Have a look at the example request at
https://mesosphere.github.io/marathon/docs/generated/api.html#v2_groups_post
and the constraints syntax at
https://mesosphere.github.io/marathon/docs/constraints.html
e.g.
"constraints": [["hostname", "CLUSTER", "slave-1"]]
should do. Downside is that there will be no automatic failover to another slave that way. Still, I'd be curious why both apps need to specifically run on the same slave node...
My application runs on 2 physical servers hosting 3 managed servers in a cluster. We have 2 Databases that are not clustered. I would like to configure the connection pools in such a way that all managed servers in Physical Machine A will go to DB1, and on failover goes to DB2. Similarily Machine B goes to DB2 always , moved to DB1 on failover. How do i configure the Connection Pool to acheive this desired behavior.
I haven't tried this but a MultiDatasource seems to be what you're looking for.
Note this is not a MultiPool since that will pick up from any of the pools based on Load Balancing or High Availability.
Define 2 Datasources, one for DB1 and one for DB2.
MultiDataSource allows you to pick up from either Datasource based on Failover or Load Balancing algorithm
http://albinoraclesoa.blogspot.in/2012/02/jdbc-multi-data-sources-in-weblogic.html
I have a question regarding Clustering (session replication/failover) in tomcat 6 using BackupManager. Reason I chose BackupManager, is because it replicates the session to only one other server.
I am going to run through the example below to try and explain my question.
I have 6 nodes setup in a tomcat 6 cluster with BackupManager. The front end is one Apache server using mod_jk with sticky session enabled
Each node has 1 session each.
node1 has a session from client1
node2 has a session from client2
..
..
Now lets say node1 goes down ; assuming node2 is the backup, node2 now has two sessions (for client2 and client1)
The next time client1 makes a request, what exactly happens ?
Does Apache "know" that node1 is down and does it send the request directly to node2 ?
=OR=
does it try each of the 6 instances and find out the hard way who the backup is ?
Not too sure about the workings with BackupManager, my reading of this good URL suggests the replication is intelligent enough in identifying the backup.
In-memory session replication, is
session data replicated across all
Tomcat instances within the cluster,
Tomcat offers two solutions,
replication across all instances
within the cluster or replication to
only its backup server, this solution
offers a guaranteed session data
replication ...
SimpleTcpCluster uses Apache Tribes to maintain communicate with the communications group. Group membership is established and maintained by Apache Tribes, it handles server crashes and recovery. Apache Tribes also offer several levels of guaranteed message delivery between group members. This is achieved updating in-session memory to reflect any session data changes, the replication is done immediately between members ...
You can reduce the amount of data by
using the BackupManager (send only to
one node, the backup node)
You'll be able to see this from the logs if notifyListenersOnReplication="true" is set.
On the other hand, you could still use DeltaManager and split your cluster into 3 domains of 2 servers each.
Say these will be node 1 <-> node 2, 3 <-> 4 and 5 <-> 6.
In such a case - configuring the domain worker attribute, will ensure that session replication will only happen within the domain.
And mod_jk then definitely knows which server to look on when node1 fails.
http://tomcat.apache.org/tomcat-6.0-doc/cluster-howto.html states
Currently you can use the domain
worker attribute (mod_jk > 1.2.8) to
build cluster partitions with the
potential of having a more scaleable
cluster solution with the
DeltaManager(you'll need to configure
the domain interceptor for this).
And a better example on this link:
http://people.apache.org/~mturk/docs/article/ftwai.html
See the "Domain Clustering model" section.
I am planning to deploy my web app to EC2. I have several webserver instances. I have 1 primary database instance. I have 1 failover database instance. I need a strategy to redirect the webservers to the failover database instance IP when the primary database instance fails.
I was hoping I could use an Elastic IP in my connection strings. But, the webservers are not able to access/ping the Elastic IP. I have several brute force ideas to solve the problem. However, I am trying to find the most elegant solution possible.
I am using all .Net and SQL Server. My connection strings are encrypted.
Does anybody have a strategy for failing over a database instance in EC2 using some form of automation or DNS configuration?
Please let me know.
http://alestic.com/2009/06/ec2-elastic-ip-internal
tells you how to use the Elastic IP public DNS.
Haven't used EC2 but surely you need to either:
(a) put your front-end into some custom maintenance mode, that you define, while you switch the IP over; and have the front-end perform required steps to manage potential data integrity and data loss issues related to the previous server going down and the new server coming up when it enters and leaves your custom maintenance mode
OR, for a zero down-time system:
(b) design the system at the object/relational and transaction levels from the ground up to support zero-down-time fail-over. It's not something you can bolt on quicjkly to just any application.
(c) use some database support for automatic failover. I am unaware whether SQL Server support for failover suitable for your application exists or is appropriate here. I suggest adding a "sql-server" tag to the question to start a search for the right audience.
If Elastic IPs don't work (which sounds odd to say the least - shouldn't you talk to EC2 about that), you mayhave to be able to instruct your front-end which new database IP to use at the same time as telling it to go from maintenance mode to normal mode.
If you're willing to shell out a bit of extra money, take a look at Rightscale's tools; they've built custom server images and supporting tools that handle database failover (among many other things). This link explains how to do it with MySQL, so will hopefully show you some principles even though it doesn't use SQL Server.
I always thought there was this possibility in the connnection string
This is taken (but not yet tested) from How to add Failover Partner to a connection string in VB.NET :
If you connect with ADO.NET or the SQL
Native Client to a database that is
being mirrored, your application can
take advantage of the drivers ability
to automatically redirect connections
when a database mirroring failover
occurs. You must specify the initial
principal server and database in the
connection string and the failover
partner server.
Data Source=myServerAddress;Failover Partner=myMirrorServerAddress;
Initial Catalog=myDataBase;Integrated Security=True;
There is ofcourse many other ways to
write the connection string using
database mirroring, this is just one
example pointing out the failover
functionality. You can combine this
with the other connection strings
options available.
To broaden gareth's answer, cloud management softwares usually solve this type of problems. RightScale is one of them, but you can try enStratus or Scalr (disclaimer: I work at Scalr). These tools provide failover solutions like:
Backups: you can schedule automated snapshots of the EBS volume containing the data
Fault-tolerant database: in the event of failure, a slave is promoted master and mounted storage will be switched if the failed master and new master are in the same AZ, or a snapshot taken of the volume
If you want to build your own solution, you could replicate the process detailed below that we use at Scalr:
Is there a slave in the same AZ? If so, promote it, switch EBS
volumes (which are limited to a single AZ), switch any ElasticIP you
might have, reconfigure replication of the remaining slaves.
If not, is there a slave fully replicated in another AZ? If so, promote it,
then do the above.
If there are no slave in same AZ, and no slave fully
replicated in another AZ, then create a snapshot from master's
volume, and use this snapshot to create a new volume in an AZ where a
slave is running. Then do the above.