Understanding Elasticsearch deployment in 2 server load balanced setup - elasticsearch

We have a two server load balanced ASP.NET MVC application that we're look to add search to - we like the look of Elasticsearch!
I'd like to build a bit of resiliency in so am considering installing ES on both servers and have them work like a cluster (which seems straightforward enough according the docs).
But I really want my MVC app to talk to "the cluster" not to each specific ES node, so if an ES node fails, or a server fails the application is unaffected:
Do I need to refer to the cluster in a special way from my application or setup some kind of internal domain for it?
I don't want to refer to "localhost:9200" or a server specific IP in my application I presume?

You should consider using the Elasticsearch .NET Client NEST. This client has built in support for failover connections when accessing an Elasticsearch Cluster.
If you want a failover client instead of passing a Uri pass an IConnectionPool see the Elasticsearch.Net documentation on cluster failover all of its implementations can also be used with NEST.

Related

Should I use Java or Logstash to index db content in Elastic Search?

I'm building a simple web application that will list/search retail items for sale.
design is like this ...
MySQL database -> Elastic Search deployment -> Spring Boot REST service -> Web UI (JSP/Bootstrap or Angular)
I am planning to write Java client code to read the database and post records to Elastic Search for indexing.
Googling, it looks like Logstash is used for this sort of thing. I'm not familiar with Logstash, I am very familiar with Java.
QUESTION: Is Java client considered a "deprecated" or "legacy" way to submit data to Elastic Search for indexing?
I'm very familiar with Java, should I use Java or Logstash?
Adding to #chris answer, logstash will add complexity and another Infrastructure to maintain in your stack, and logstash is known for getting stuck and is not as resilient as Elasticsearch is.
You are already using Java for your application code and btw elasticsearch now officially has a java client known as java high-level rest client(JHLRC) , which is very popular and provides an exhaustive list of APIs for indexing/searching and building a modern search system.
IMHO you should use the JHLRC,
which will save you to the pain points of logstash
you don't have to learn another tool
simple infrastructure
simple deployment
last but not least simple and easy to maintain codebase.
Logstash is good tool to be used to migrate the data from many sources to elastic search. It's build in java language only.
You can use Logstash. It also has options to mutate the data or filter the data. Its a ready to use to tool which will save lot of your development time and efforts.
But if you have a requirement for lot of customisation and need lot of control over your data before pushing it to elastic search then you can build your own application for the same.
Coming back to your question..java is not deprecated for indexing data to elastic search. It is still a preferred option.

Proper crawler architecture - how to using ElasticSearch ecosystem?

In a v1.0 of a .Net data crawler, I created a Windows service that would read URLs from a database and based on some logic would select what to crawl on a specified interval.
This was single-threaded and worked well for a low number of endpoints, but scaling is obviously an issue.
I'm trying to find out how to do this using the ElasticSearch (ELK) stack and came across HTTPBeat,
a Beat to poll HTTP endpoints in a regular interval and ship the
result to the configured output channel, e.g. Logstash and
Elasticsearch.
In looking at the documentation, you have to add URLs to the config.yaml file. Not what I'm looking for as the list of URLs could change and we may not want all URLs crawled at the same time.
Then there's RSS for Logstash, which is a command-line tool - again, not what I'm looking for.
Is there a way to make use of the Beats daemon to read from the ElasticSearch database to do work based on database values - crawls, etc?
To take this to the enterprise level, do Beats or any other component of the ElasticSearch ecosystem use message queuing or a spooler (like FileBeats does - is this built into Beats?)?

How can a Phoenix application tailored only to use channels scale on multiple machines? Using HAProxy? How to broadcast messages to all nodes?

I use the node application purely for socket.io channels with Redis PubSub, and at the moment I have it spread across 3 machines, backed by nginx load balancing on one of the machines.
I want to replace this node application with a Phoenix application, and I'm still all new to the erlang/Elixir world so I still haven't figured out how a single Phoenix application can span on more than one machine. Googling all possible scaling and load balancing terms yielded nothing.
The 1.0 release notes mention this regarding channels:
Even on a cluster of machines, your messages are broadcasted across the nodes automatically
1) So I basically deploy my application to N servers, starting the Cowboy servers in each one of them, similarly to how I do with node and them I tie them nginx/HAProxy?
2) If that is the case, how channel messages are broadcasted across all nodes as mentioned on the release notes?
EDIT 3: Taking Theston answer which clarifies that there is no such thing as Phoenix applications, but instead, Elixir/Erlang applications, I updated my search terms and found some interesting results regarding scaling and load balancing.
A free extensive book: Stuff Goes Bad: Erlang in Anger
Erlang pooling libraries recommendations
EDIT 2: Found this from Elixir's creator:
Elixir provides conveniences for process grouping and global processes (shared between nodes) but you can still use external libraries like Consul or Zookeeper for service discovery or rely on HAProxy for load balancing for the HTTP based frontends.
EDITED: Connecting Elixir nodes on the same LAN is the first one that mentions inter Elixir communication, but it isn't related to Phoenix itself, and is not clear on how it related with load balancing and each Phoenix node communicating with another.
Phoenix isn't the application, when you generate a Phoenix project you create an Elixir application with Phoenix being just a dependency (effectively a bunch of things that make building a web part of your application easier).
Therefore any Node distribution you need to do can still happen within your Elixir application.
You could just use Phoenix for the web routing and then pass the data on to your underlying Elixir app to handle the distribution across nodes.
It's worth reading http://www.phoenixframework.org/v1.0.0/docs/channels (if you haven't already) where it explains how Phoenix channels are able to use PubSub to distribute (which can be configured to use different adapters).
Also, are you spinning up cowboy on your deployment servers by running mix phoenix.server ?
If so, then I'd recommend looking at EXRM https://github.com/bitwalker/exrm
This will bundle your Elixir application into a self contained file that you can simply deploy to your production servers (with Capistrano if you like) and then you start your application.
It also means you don't need any Erlang/Elixir dependencies installed on the production machines either.
In short, Phoenix is not like Rails, Phoenix is not the application, not the stack. It's just a dependency that provides useful functionality to your Elixir application.
Unless I am misunderstanding your use case, you can still use the exact scaling technique your node version of the application is. Simply deploy the Phoenix application to > 1 machines and use an Nginx load balancer configured to forward requests to one of the many application machines.
The built in node communications etc of Erlang are used for applications that scale in a different way than a web app. For instance, distributed databases or queues.
Look at Phoenix.PubSub
It's where Phoenix internally has the Channel communication bits.
It currently has two adapters:
Phoenix.PubSub.PG2 - uses Distributed Elixir, directly exchanging notifications between servers. (This requires that you deploy your application in a elixir/erlang distributed cluster way.)
Phoenix.PubSub.Redis - uses Redis to exchange data between servers. (This should be similar to solutions found in socket.io and others)

Websphere application server 8.5.5 clustering same application

I have the same application running on two WAS clusters. Each cluster has 3 application servers based in different datacenters. In front of each cluster are 3 IHS servers.
Can I specify a primary cluster, and a failover cluster within the plugin-cfg.xml? Currently I have both clusters defined within the plugin, but I'm only hitting 1 cluster for every request. The second cluster is completely ignored.
Thanks!
As noted already the WAS HTTP server plugin doesn't provide the function your're seeking as documented in the WAS KC http://www-01.ibm.com/support/knowledgecenter/SSAW57_8.5.5/com.ibm.websphere.nd.doc/ae/rwsv_plugincfg.html?lang=en
assuming that by "failover cluster" what is actually meant is "BackupServers" in the plugin-cfg.xml
The ODR alternative mentioned previously likely isn't an option either, this because the ODR isn't supported for use in the DMZ (it's not been security hardened for DMZ deployment) http://www-01.ibm.com/support/knowledgecenter/SSAW57_8.5.5/com.ibm.websphere.nd.doc/ae/twve_odoecreateodr.html?lang=en
From an effective HA/DR perspective what you're seeking to accomplish should handled at the network layer, using the global load balancer (global site selector, global traffic manager, etc) that is routing traffic into the data centers, this is usually accomplished by setting a "site cookie" using the load balancer
This is by design. IHS, at least at the 8.5.5 level, does not allow for what you are trying to do. You will have to implement such level of high availability in a higher level in your topology.
There are a few options.
If the environemnt is relatively static, you could post-process plugin-cfg.xml and combine them into a single ServerCluster with the "dc2" servers listed as <BackupServer>'s in the cluster. The "dc1" servers are probably already listed as <PrimaryServer>'s
BackupServers are only used when no PrimaryServers are reachable.
Another option is to use the Java On-Demand Router, which has first-class awareness of applications running in two cells. Rules can be written that dictate the behavior of applications residing in two clusters (load balancer, failover, etc.). I believe these are "ODR Routing Rules".

using elasticsearch replications in django

The current setup is compose by 3 elastic search servers, of witch one is the master and the other 2 are slave, at least they define themselves as that.
It might happen that the master goes down, for any kind of problem, this means that elastic search is going to find a new elegible master and switch to this new one.
Currently the problem is that all my application on the frontend servers is totally not aware of this so it will keel making queries to the same backend, of course killing all my website because it will not answer. I had a look around but I was not able to find anything related to backend switch on the fly even related to the new Haystack 2.x.
Any suggestion?
Many thanks in advance
It doesn't seem to be necessary to me to leave this to your application layer. Most probably you access ES through HTTP-REST requests, which means you can put any HTTP load balancer like Nginx in front of your ES servers which should also switch to another node if one times out.

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