NewRelic error with spring boot

 Recently we added two datasources to our application and our application worked fine without newRelic. But as soon as we added newRelic to our application it failed with a strange error:

2024-11-08 20:22:37 java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0
2024-11-08 20:22:37     at org.jboss.jandex.Indexer.updateTypeTarget(Indexer.java:903)
2024-11-08 20:22:37     at org.jboss.jandex.Indexer.updateTypeTargets(Indexer.java:630)
2024-11-08 20:22:37     at org.jboss.jandex.Indexer.index(Indexer.java:1698)
2024-11-08 20:22:37     at org.hibernate.boot.archive.scan.spi.ClassFileArchiveEntryHandler.toClassDescriptor(ClassFileArchiveEntryHandler.java:64)
2024-11-08 20:22:37     at org.hibernate.boot.archive.scan.spi.ClassFileArchiveEntryHandler.handleEntry(ClassFileArchiveEntryHandler.java:52)
2024-11-08 20:22:37     at org.hibernate.boot.archive.internal.JarFileBasedArchiveDescriptor.visitArchive(JarFileBasedArchiveDescriptor.java:147)
2024-11-08 20:22:37     at org.hibernate.boot.archive.scan.spi.AbstractScannerImpl.scan(AbstractScannerImpl.java:48)
2024-11-08 20:22:37     at org.hibernate.boot.model.process.internal.ScanningCoordinator.coordinateScan(ScanningCoordinator.java:76)
2024-11-08 20:22:37     at org.hibernate.boot.model.process.spi.MetadataBuildingProcess.prepare(MetadataBuildingProcess.java:107)
2024-11-08 20:22:37     at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.<init>(EntityManagerFactoryBuilderImpl.java:269)
2024-11-08 20:22:37     at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.<init>(EntityManagerFactoryBuilderImpl.java:182)
2024-11-08 20:22:37     at org.springframework.orm.jpa.vendor.SpringHibernateJpaPersistenceProvider.createContainerEntityManagerFactory(SpringHibernateJpaPersistenceProvider.java:52)
2024-11-08 20:22:37     at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:365)
2024-11-08 20:22:37     at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.buildNativeEntityManagerFactory(AbstractEntityManagerFactoryBean.java:409)
2024-11-08 20:22:37     at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:396)
2024-11-08 20:22:37     at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.afterPropertiesSet(LocalContainerEntityManagerFactoryBean.java:341)
2024-11-08 20:22:37     at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1863)
2024-11-08 20:22:37     at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1800)

After struggling for a lot of time we figured out that one of the datasource was not having any entity defined. After defining a dummy entity for the datasource the error was gone away and the application started working with newRelic also.

Please do comment if you find it useful.

Adding CORS headers to python flask server

 Recently we were trying to add CORS headers to a python flask web server to allow our react website to be allowed to make call to APIs hosted in python flask server. Our aim was to make least amount of code change to server and incorporate CORS headers in all the APIs hosted on this server. We tried for 2-3 days and found a really simple ways of doing it.

Here I am sharing the solution. We added a after request handler in flask to add required headers to all the responses after the response is generated.

from flask import Flask
from flask_restful import Resource, Api

app = Flask(__name__)
api = Api(app)

class HelloWorld(Resource):
    def get(self):
        return {'hello': 'world'}

api.add_resource(HelloWorld, '/')

@app.after_request
def add_cors_header(response):
    response.headers["Access-Control-Allow-Origin"] = "*"
    response.headers["Access-Control-Allow-Headers"] = "*"
    return response

if __name__ == '__main__':
    app.run(debug=False)

Allowing Client to Client connect on VPN

Recently we were trying to debug an application with two developers one backend developer and one frontend developer. We were working in work from home setup so both were working from home.

We were wasting a lots of effort in pushing backed changes again and again to our staging server for testing. We were thinking that it would be great if frontend developer could connect to service running on backend developer's machine directly and debug the problem. We tried connecting using private IP address of backend developer's machine but connection timed out.

Later on we discovered that there was a configuration needed on OpenVpn server. You need to enable following configuration on OpenVpn server to enable client to client connection. We found this functionality to be of a great help in debugging.

client-to-client

Following post was very useful https://serverfault.com/questions/570316/how-can-multiple-clients-of-an-openvpn-server-find-each-other

Same can be achieved in AWS client VPN also https://docs.aws.amazon.com/vpn/latest/clientvpn-admin/scenario-client-to-client.html

java.time.ZonedDateTime not supported in ObjectMapper

Recently I was trying to serialize a Java object into json using ObjectMapper but encountered the following exception

com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Java 8 date/time type `java.time.ZonedDateTime` not supported by default: add Module "com.fasterxml.jackson.datatype:jackson-datatype-jsr310" to enable handling

The reason was that Java time module is not supported by default and it does not work just by adding maven dependency. The following code worked for me.

objectMapper = new ObjectMapper();
objectMapper.registerModule(new JavaTimeModule());
objectMapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);

Finding mongo documents with lowercase values in a mongo collection

Recently we were trying to make our mongo DB based application case insensitive and for testing we needed to find all document containing lowercase alphabets in a filed called "sku". The following query was able to do the work.

{"$expr": {"$ne": ["$sku", {"$toUpper": "$sku"}]}}

Please note that this query does not work on AWS DocumentDB.