How to properly implement load balancer healthcheck for Grails - grails

Question

I'm working with a Grails 2 application that is deployed to Amazon AWS which uses a software load balancer (ELB). The problem we are having is that the grails application instances are added to the load balancer before the application is fully initialized. It's the resources plugin specifically which serves static assets like javascript, css, images, etc.
The load balancer makes an http request to a 'healthcheck' URL.
GET '/myapp/lbcheck'
LoadBalancerController.groovy:
package myapp
class LoadBalancerController {
def healthService
def healthcheck() {
response.contentType = 'text/plain'
try {
healthService.checkDatabase()
render(status: 200, text: "Up")
}
catch(Exception ex) {
log.error("Error with database healthcheck " + ex)
render(status: 503, text: "Down")
}
}
}
HealthSerivce.groovy
package myapp
import groovy.sql.Sql
class HealthService {
def dataSource
// Either returns true, or throws an Exception
def checkDatabase() {
Sql sql = new Sql(dataSource)
sql.rows("SELECT 429")
sql.close()
return true
}
}
The SQL query clearly isn't enough. It seems like we need to check some other kind of property in the framework to determine that it has been initialized.

Answer 1

You could try setting setting a field on your healthService bean to true inside of BootStrap.groovy. I think that's run after Grails is fully initialized.
package myapp
import groovy.sql.Sql
class HealthService {
def dataSource
def initializationComplete = false
// Either returns true, or throws an Exception
def checkDatabase() {
Sql sql = new Sql(dataSource)
sql.rows("SELECT 429")
sql.close()
return true
}
}
inside BootStrap.groovy:
class BootStrap {
def healthService
def init = { servletContext ->
healthService.initializationComplete = true
}
}
in your LoadBalancerController.groovy:
def healthcheck() {
response.contentType = 'text/plain'
def healthy = false
try {
healthy = healthService.with {
initializationComplete && checkDatabase()
}
}
catch(Exception ex) {
log.error("Error with database healthcheck " + ex)
}
if (healthy) {
render(status: 200, text: "Up")
} else {
render(status: 503, text: "Down")
}
}