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Manage running Java apps remotely

We have several Java standalone applications (in form of Jar files) running on multiple servers. These applications mainly read and stream data between systems. We are using Java 8 mainly in our development. I was put in charge recently. My main function is to manage and maintain these apps.
Currently, I check these apps manually by accessing these servers, check if the app is running, and sometimes run some database queries to see if the app started pulling data. My problem is that in many cases, some of these apps fail and shutdown due to data issue or edge cases without anyone noticing. We need some monitoring and application recovery in place.
We don't have docker infrastructure in place. We plan to implement docker in the future, but for now this is not an option.
After research, the following are options I thought of or solutions I tried:
Have the apps create a socket client which sends a heartbeat to a monitoring app (which needs to be developed). I am keeping this as my last option.
I tried to use Eclipse Vertx to wrap the apps into Verticles. Then create a web view that can show me status and other info. After several tries, the apps fail to parse the data correctly (might be due to my lack of understanding to Vertx library).
Have a third party solution that does this, but I have no idea what solutions are out there. I am open for suggestions.
My requirements are:
Proper monitoring of the apps running and their status.
In case of failure, the app should start again while notifying the admin/developer.
I am willing to develop a solution or implement a third party one. I need you guidance on this.
Thank you.

You could use spring-boot-actuator (see health). It comes with a built-in endpoint that has some health checks(depending on your spring-boot project), but you can create your own as well.
Then, doing a http request to http://{host}:{port}/{context}/actuator/health (replace with yours), you could see those health checks status and also use the response status code to monitor your application.

Have you heard of Java Service Wrappers? Not a full management functionality, however it would monitor for JVM crashes and out of memory conditions and restart your application for sure. Alerting should also be possible.
There is a small comparison table here: https://yajsw.sourceforge.io/#mozTocId284533
So some basic monitoring and management is included already. If you need more, I suggest using JMX (https://www.oracle.com/java/technologies/javase/javamanagement.html) or Prometheus (https://prometheus.io/ and https://github.com/prometheus/client_java)

Find out whose using Redis

We have one Redis for our company and multiple teams are using it. We are getting a surge of requests and nobody seems to know which application is causing it. We have only one password that goes around the whole company and our Redis is secured under a VPN so we know it's not coming from the outside.
Is there a way to know whose using Redis? Maybe we can pass in some headers with the connection from every app to identify who makes the most requests, etc.
We use Spring Data Redis for our communication.

This question is too broad since different strategies can be used here:
Use Redis MONITOR command. This is basically a built-in debugging tool that monitors all the commands executed by Redis
Use some kind of intermediate proxy. Instead of routing all the commands directly to redis - route everything to proxy that will do some processing like measuring the amounts of commands by the calling host or maybe types of commands depending what you want.
This is still only a configuration related solution so you won't need any changes at the level of applications
Since you have spring boot, you can use Micrometer / metering integration. This way you could create a counter / gauge that will get updated upon each request to Redis. If you also stream the metering data to tools like Prometheus, you'll be able to create a dashboard, say in grafana to see the whole picture. Micrometer can integrate also with other products, Prometheus/Grafana was only an example, you can chose any other solution (maybe in your organization you already have something like that).

Restful Webservices using Java, Apache Axis2, Hibernate and MySQL and its performance

I read somewhere use of webservcies in apps. After a lot of research I am able to create one Webservice which will accept Json and JsonP both format as request and response accordingly. I developed the webservcies using Java, Apache Axis2, Hibernate and MySQL as database. there are few problems and I dont know how to solve ?
Insert or delete option, sometimes if at a time more than two users call that service that is insert or delete any row the queries go in sleep mode and next time someone tries to fetch that service he couldnt. Accroding to server log it says error SQL Lockout State. If I checks Processlist in MYSQL it is showing that query in Sleep, I have to kill to resume.
The performance of webservice doesnt seems to be upto mark, it takes time some more time as what i experienced it shouldn't. In simple words how to obtain better performance by the services
How to implement security feature such that if a user logins he/she can be provided an id and validation of that id so that unauthorized access can be prevented
Or just guide me what should be the most appropriate and optmized Webservice methodology that can be used using Java

Answer to this question is not specific to Android. Below are my investigations which might be useful for you.
For the point about MySQL connections going to sleep mode, you can do the following.
Debug the datasource used by Hibernate, try to increase the pool size & check for any issues in it.
Define a timeout period for connections. JBoss has several configurations related to this like blocking-timeout-millis, idle-timeout-minutes etc.
Declare a mechanism to validate periodically the connection resources in the pool for activeness. You can explore OracleStaleConnectionChecker for options.
Configure miniumn connections in the pool. This is important because when all the stale connections are discarded, empty pool needs to be pre-filled & ready with active connections.
Coming to performance of Insert/Delete operations & SQL Lockout State, please try to re-order the sequence of the queries which you are firing to DB at every request. This may not be a deadlock situation but sequencing DB queries correctly will definitely lead to less lockout time and better performance.
This answer may be of use for you. Hibernate: Deadlock found when trying to obtain lock
Web-services which you have developed may require some performance optimization to make them upto the mark. Below are first few steps you can take to bring the performance up.
Avoid nested loops. Every extra parameter in the iterated lust increase the order of the lopp exponentially.
Remove early initialization of objects. This may lead to long unwanted GC cycles.
Apart from above optimizations, there are several frameworks & tools at your service to evaluate the code quality & its performance. PMD, FindBugs, JMeter, Java profiler are few of them to name.
Shishir

You are going to have to profile your server and see where the time is spent. I really like YourKit for doing thread profile. visualvm which comes with the JDK can help also.
There are all sorts of reasons your web service can be slow:
Latency from client to server
Handling the HTTP request on the server
Handling the HTTP response on the client
Making the database call (sounds like you already have some kind of locking / blocking going on there)
You are going to have to get markers to tell you how long it took to go from A to B to C to D back to C back to B back to A kind of thing. We would be speculating heavily from here on what is exactly going on in your program, but we can give you the ideas / tools to figure it out.
If you use YourKit, connect it to your server process. Have nothing else connecting to your server (for instance your client is not sending requests). Try it with your client requesting, you should see your accepting threads receive the HTTP request and then delegate to either your processing thread or do the processing itself. You can use YourKit to see how much time is spent in different functions during that call time.
Try it with your client making the call.
Try it using a simple HTTP request tool like wget or maybe your IDE has a webservice test tool (for instance intellij does), or you can download a simple HTTP test tool.
By testing it in a simple tool that just outputs the response, you can eliminate any client processing issues. You can also achieve a similar test in Chrome or Firefox and use the developer tools to see time to fulfill request.
In my experience, the framework for handling the requests and delegating can introduce some performance issues. I ripped Grails out of a production environment because of its performance issues (before any Grails / Groovy flames come my way, we were operating at a much higher rate than typical web applications, and I am sure Grails has made some headway in the last couple years... alas, it was not for my need at that time)
BTW, I doubt you are operating a load where you will be critiquing the web service framework you chose to use. I have been happy with Spring MVC and DropWizard (Jersey JAX-RS), and Grails is easy to use too.
You should make a simple static content response in your webservice and see how quickly that returns vs a request that makes a database call.
Also, what kind of table are you using in MySQL? InnoDB? MyISAM? They have different locking schemes. That could be causing your MySQL issue.
The key to all of it, break the problem up into parts, and measure each and eliminate parts one by one till you go, everytime I do X it is slower (like everytime I make a database call its slower)

In Java the the way you will be able to find more support online via documentation/forums is to develop the web service as a REST web service using Spring MVC.
You can base yourself on this resource and take it from there:
Spring MVC REST Hello World Web Service

Using Spring you can create a RestFul webservice easily and spring does all the ground work you needed. As others had mentioned you can consume the webservice in any type of client - including Android.
A detailed guide available here:
https://spring.io/guides/gs/rest-service/

Here are my suggestions:
Make APIs only read or write database. If an API combines reading and writing, it is possible to cause deadlock;
Use a light-weight HTTP server. Powerful HTTP server is possibly consuming more.
Make use of thread. Have more threads could be helpful when you are facing a ton of users.
Make more things static. You could avoid unnecessary queries.
I think mhoglan's answer is detailed enough.

Non-container based java remoting?

We're trying to design a new addition to our application. Basically we need to submit very basic queries to various remote databases accessed over the internet and not owned or controlled by us.
Our proposal is to install a small client app on each of the foreign systems, tiered in 2 basic layers, 1 that is tailored to the particular database its talking to, to handle the actual query in SQL or whatever, the other tier would be the communication tier to handle incoming requests and send back responses. This communication interface would be the same over all of the foreign systems, ie all requests and responses have the same structure.
In terms of java remoting I guess this small client app would be the 'server' and our webapp (normally referred to as the server) is the 'client'.
I've looked at various java remoting solutions (Hessian, Burlap, RMI, SOAP/REST WebServices). However am I correct in thinking that with all of these the 'server' must run in a container, ie in a tomcat/jetty etc instance?
I was really hoping to avoid having to battle all the IT departments controlling the foreign systems to get them to install very much. The whole idea is that its thin/small/easy to install/pain free. Are there any solutions that do not require running in a container / webserver?
The communication really is the smallest part of this design, no more than 10 string input params (that have no meaning other than to the db) and one true/false output. There are no complex object models required. The only complexity would be from security/encryption etc.

I wamly suggest somethig based on Jetty, the embedded HTTP server. You package a simple runnable JAR with dependency JARs into a ZIP file, add a startup script, and you have your product. See for example here.

I often use Sprint-Remoting in my projects and here you find a description how to use without a container. The guy is starting the jetty from within his application:
http://forum.springsource.org/showthread.php?12852-HttpInvoker-without-web-container
http://static.springsource.org/spring/docs/2.0.x/reference/remoting.html
Regards,
Boskop

Yes, most of them runs a standard servlet container. But containers like Jetty have very low footprint and you may configure and run Jetty completely out of your code while you stay with servlet standards.
Do not fail to estimate initial minimal requirements that may grow with project enhancement over time. Then have a standard container makes things much more easier.

As you have tagged this question with [rmi], RMI does not require any form of container. All you need is the appropriate TCP ports to be open.

JMX scalabilty: can it be used to manage 400+ instances?

I'm evaluating solutions for managing 400+ instances of a kiosk-like application. Each instance runs a custom Java application that displays information and interacts with users. We are pondering if we should develop a custom solution, try to include JMX support for it or find something else.
The requirements are simple:
It must be a free and open source solution;
It must be able to manage more than 400 instances (for example: one manager managing 400 JMX-enabled clients);
It should be preferably programmed in Java;
We need standard metrics (for example: available resources, running times, current status, etc);
Optionally we would like to send some control messages to the instances.
It seems that JMX features and flexibility is what we were looking for. However, I haven't found much about JMX scalability. How many "clients" can one JMX manager handle? Is it possible to manage 400 JMX instances concurrently? Is there any recommended architecture or workaround if it doesn't handle so many clients directly?
Thanks for any hints

JMX is exactly what you want.
As far as how many clients you can connect to, I'd imagine that for the monitoring portions of it, you'd only really need to fetch data from the remote clients every few seconds, at the most, right?
I'm not sure if a solution already exists which will allow you to monitor N clients and also control them, so you'd likely want to develop something yourself - interacting with remote MBeans with JMX code seems to be trivial, which then turns this into an exercise of being able to write a program which can concurrently communicate with 400 nodes successfully.