Switch cache directories to EmptyDir by default

When using PVCs for cache directories, each pod requires two PVCs. This easily leads to exhaustion of the maximum number of mounted volumes per node (see [Node-specific Volume Limits](https://kubernetes.io/docs/concepts/storage/storage-limits/)).

Closes #103

docs/custom-resource.md

@@ -120,6 +120,7 @@ properties have suitable defaults.
 | `licenseSecrets.RLSLicense`         | String               | `license-rls`                                     | Name of the secret containing a `license.zip` entry with the appropriate file contents                                                       |
 | `siteMappings`                      | array                | –                                                 | Mappings between DNS names and site segments, see below                                                                                      |
 | `with`                              | object               | –                                                 | Optional special components and configurations                                                                                               |
+| `with.cachesAsPvc`                 | boolean              | false                                             | Use Persistent Volume Claims when creating various cache directories, instead of EmptyDirs.                                                  |
 | `with.databases`                    | boolean              | false                                             | Create both a MariaDB and MongoDB server, and schemas and secrets for all components that require them                                       |
 | `with.databasesOverride`            | object               | –                                                 | If `with.databases` is `true`, override the creation for specific kinds.                                                                     |
 | `with.databasesOverride.`*kind*     | boolean              | true                                              | When set to `false`, do not create database and secrets for *kind*. If set to true, or the entry is missing, do create them.                 |
@@ -143,6 +144,14 @@ properties have suitable defaults.
 
 ## Enabling Convenience Options `with`
 
+### Persistent Caches `with.cachesAsPvc`
+
+By default, cache directories in UAPI components are created
+using [EmptyDir](https://kubernetes.io/docs/concepts/storage/volumes/#emptydir)s.
+
+Set this to `true` to instead use Persistent Volume Claims. This allows the caches to persist across pod restarts. Note
+however, that this requires a large number of PVCs, which might exceed the limit on your nodes.
+
 ### Local database servers `with.databases`
 
 When `with.databases` is enabled, the operator will add a MariaDB and a MongoDB server to the components, and create

src/main/java/com/tsystemsmms/cmcc/cmccoperator/components/corba/CorbaComponent.java

@@ -137,16 +137,29 @@ public List<Volume> getVolumes() {
                     .withEmptyDir(new EmptyDirVolumeSource())
                     .build()
     ));
+    if (!getCmcc().getSpec().getWith().getCachesAsPvc()) {
+      volumes.addAll(List.of(
+              new VolumeBuilder()
+                      .withName(PVC_TRANSFORMED_BLOBCACHE)
+                      .withEmptyDir(new EmptyDirVolumeSource())
+                      .build(),
+              new VolumeBuilder()
+                      .withName(PVC_UAPI_BLOBCACHE)
+                      .withEmptyDir(new EmptyDirVolumeSource())
+                      .build()
+      ));
+    }
     return volumes;
   }
 
   @Override
   public List<PersistentVolumeClaim> getVolumeClaims() {
     List<PersistentVolumeClaim> claims = super.getVolumeClaims();
 
-    claims.add(getPersistentVolumeClaim(PVC_TRANSFORMED_BLOBCACHE, getVolumeSize(ComponentSpec.VolumeSize::getTransformedBlobCache)));
-    claims.add(getPersistentVolumeClaim(PVC_UAPI_BLOBCACHE, getVolumeSize(ComponentSpec.VolumeSize::getUapiBlobCache)));
-
+    if (getCmcc().getSpec().getWith().getCachesAsPvc()) {
+      claims.add(getPersistentVolumeClaim(PVC_TRANSFORMED_BLOBCACHE, getVolumeSize(ComponentSpec.VolumeSize::getTransformedBlobCache)));
+      claims.add(getPersistentVolumeClaim(PVC_UAPI_BLOBCACHE, getVolumeSize(ComponentSpec.VolumeSize::getUapiBlobCache)));
+    }
     return claims;
   }
 

src/main/java/com/tsystemsmms/cmcc/cmccoperator/crds/WithOptions.java

@@ -23,6 +23,9 @@ public class WithOptions {
     @JsonPropertyDescription("Import content, users, themes and workflows")
     Boolean contentImport = true;
 
+    @JsonPropertyDescription("Create cache directories as Persistent Volume Claims")
+    Boolean cachesAsPvc = false;
+
     @JsonPropertyDescription("Create databases and secrets for CoreMedia")
     Boolean databases = false;