Use ConfigMapList's resourceVersion for watching (AtomicLong)

Rationale: avoid ERROR notifications during a rolling upgrade.

Using the greatest `resourceVersion` of all the `ConfigMap`s returned
within the `ConfigMapList` works as expected for *fresh* deployments.
But, when performing a *rolling upgrade*, the watcher happens to
frequently stop after having received an `ERROR` notification:
>>>
[ERROR] [KubernetesConfigMapWatcher] [] Kubernetes API returned an error
for a ConfigMap watch event: ConfigMapWatchEvent{type=ERROR,
object=ConfigMap{metadata=Metadata{name='null', namespace='null',
uid='null', labels={}, resourceVersion=null}, data={}}}
>>>
What's actually streamed in that case is a `Status` object such as:
```json
{
  "type": "ERROR",
  "object": {
    "kind": "Status",
    "apiVersion": "v1",
    "metadata": {},
    "status": "Expired",
    "message": "too old resource version: 123 (456)",
    "reason": "Gone",
    "code": 410
  }
}
```

A few references:
* ManageIQ/kubeclient#452
* https://www.baeldung.com/java-kubernetes-watch#1-resource-versions

It's possible to recover by adding some logic to reinstall the watcher
starting with the newly advertised `resourceVersion`, but this may be
avoided at all by starting initial the watch at the `resourceVersion`
of the `ConfigMapList` itself.

The proposed implementation consists in storing last received
`resourceVersion` as a side effect of `getPropertySourcesFromConfigMaps`
(inspired by how `PropertySource`s get cached through
`configMapAsPropertySource`) and later using it when installing the
watcher.

kubernetes-discovery-client/src/main/java/io/micronaut/kubernetes/client/v1/configmaps/ConfigMapList.java

@@ -16,6 +16,7 @@
 package io.micronaut.kubernetes.client.v1.configmaps;
 
 import io.micronaut.core.annotation.Introspected;
+import io.micronaut.kubernetes.client.v1.KubernetesObject;
 
 import java.util.Collections;
 import java.util.List;
@@ -28,7 +29,7 @@
  * @since 1.0.0
  */
 @Introspected
-public class ConfigMapList {
+public class ConfigMapList extends KubernetesObject {
 
     private List<ConfigMap> items;
 

kubernetes-discovery-client/src/main/java/io/micronaut/kubernetes/configuration/KubernetesConfigMapWatcher.java

@@ -37,7 +37,7 @@
 import java.util.Map;
 import java.util.concurrent.ExecutorService;
 
-import static io.micronaut.kubernetes.configuration.KubernetesConfigurationClient.KUBERNETES_CONFIG_MAP_NAME_SUFFIX;
+import static io.micronaut.kubernetes.configuration.KubernetesConfigurationClient.getLastConfigMapListResourceVersion;
 import static io.micronaut.kubernetes.util.KubernetesUtils.computePodLabelSelector;
 
 /**
@@ -80,7 +80,7 @@ public KubernetesConfigMapWatcher(Environment environment, KubernetesClient clie
     @SuppressWarnings("ResultOfMethodCallIgnored")
     @Override
     public void onApplicationEvent(ServiceReadyEvent event) {
-        long lastResourceVersion = computeLastResourceVersion();
+        long lastResourceVersion = getLastConfigMapListResourceVersion();
         Map<String, String> labels = configuration.getConfigMaps().getLabels();
         Flowable<String> singleLabelSelector = computePodLabelSelector(client, configuration.getConfigMaps().getPodLabels(), configuration.getNamespace(), labels);
 
@@ -100,23 +100,6 @@ public void onApplicationEvent(ServiceReadyEvent event) {
                 .subscribe(this::processEvent);
     }
 
-    private long computeLastResourceVersion() {
-        long lastResourceVersion = this.environment
-                .getPropertySources()
-                .stream()
-                .filter(propertySource -> propertySource.getName().endsWith(KUBERNETES_CONFIG_MAP_NAME_SUFFIX))
-                .map(propertySource -> propertySource.get(KubernetesConfigurationClient.CONFIG_MAP_RESOURCE_VERSION))
-                .map(o -> Long.parseLong(o.toString()))
-                .max(Long::compareTo)
-                .orElse(0L);
-
-        if (LOG.isDebugEnabled()) {
-            LOG.debug("Latest resourceVersion is: {}", lastResourceVersion);
-        }
-
-        return lastResourceVersion;
-    }
-
     private void processEvent(ConfigMapWatchEvent event) {
         switch (event.getType()) {
             case ADDED:

kubernetes-discovery-client/src/main/java/io/micronaut/kubernetes/configuration/KubernetesConfigurationClient.java

@@ -42,6 +42,7 @@
 import java.nio.file.Paths;
 import java.util.*;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicLong;
 
 import static io.micronaut.kubernetes.client.v1.secrets.Secret.OPAQUE_SECRET_TYPE;
 import static io.micronaut.kubernetes.util.KubernetesUtils.computePodLabelSelector;
@@ -66,6 +67,7 @@ public class KubernetesConfigurationClient implements ConfigurationClient {
     private static final Logger LOG = LoggerFactory.getLogger(KubernetesConfigurationClient.class);
 
     private static Map<String, PropertySource> propertySources = new ConcurrentHashMap<>();
+    private static AtomicLong lastConfigMapListResourceVersion = new AtomicLong();
 
     private final KubernetesClient client;
     private final KubernetesConfiguration configuration;
@@ -140,6 +142,13 @@ static Map<String, PropertySource> getPropertySourceCache() {
         return propertySources;
     }
 
+    /**
+     * @return the last config map list resource version.
+     */
+    static long getLastConfigMapListResourceVersion() {
+        return lastConfigMapListResourceVersion.get();
+    }
+
     private Flowable<PropertySource> getPropertySourcesFromConfigMaps() {
         Predicate<KubernetesObject> includesFilter = KubernetesUtils.getIncludesFilter(configuration.getConfigMaps().getIncludes());
         Predicate<KubernetesObject> excludesFilter = KubernetesUtils.getExcludesFilter(configuration.getConfigMaps().getExcludes());
@@ -150,9 +159,11 @@ private Flowable<PropertySource> getPropertySourcesFromConfigMaps() {
                 .doOnError(throwable -> LOG.error("Error while trying to list all Kubernetes ConfigMaps in the namespace [" + configuration.getNamespace() + "]", throwable))
                 .onErrorReturn(throwable -> new ConfigMapList())
                 .doOnNext(configMapList -> {
+                    final String resourceVersion = configMapList.getMetadata().getResourceVersion();
                     if (LOG.isDebugEnabled()) {
-                        LOG.debug("Found {} config maps. Applying includes/excludes filters (if any)", configMapList.getItems().size());
+                        LOG.debug("Found {} config maps in list version {}. Applying includes/excludes filters (if any)", configMapList.getItems().size(), resourceVersion);
                     }
+                    lastConfigMapListResourceVersion.set(Long.parseLong(resourceVersion));
                 })
                 .flatMapIterable(ConfigMapList::getItems)
                 .filter(includesFilter)