improve minecraft performance by using a non nfs volume for live data

apps/minecraft/README.md

@@ -1,3 +1,11 @@
+## Setup
+Because minecraft is quite sensitive to io performance, we want the data to be stored on a local disk. But hostpath is not well supported in talos (and is not persistent), so we use an ephemeral volume instead. In order to do this, we create an emptyDir volume and mount it to the pod.
+
+We use an initContaier that copies the data to the local storage. Afterwards, copying from the local storage back to the persistent storage is handled by a preStop lifecycle event.
+
+This way, we can have the best of both worlds: fast local storage and persistent storage.
+
+
 ## Sending a command
 ```
 kubectl exec -it -n minecraft deploy/minecraft-server -- /bin/bash

apps/minecraft/job.yaml

@@ -9,6 +9,16 @@ spec:
         app: minecraft-server
     spec:
       restartPolicy: OnFailure
+      initContainers:
+      - name: copy-data-to-local
+        image: alpine
+        command: ["/bin/sh"]
+        args: ["-c", "cp -r /data/* /local-data/"]
+        volumeMounts:
+        - name: local-data
+          mountPath: /local-data
+        - name: minecraft-data
+          mountPath: /data
       containers:
       - name: minecraft-server
         image: minecraft
@@ -49,12 +59,34 @@ spec:
           value: "false"
         - name: ENABLE_AUTOSTOP
           value: "true"
-        
+        - name: AUTOSTOP_TIMEOUT_EST
+          value: "1800" # stop 30 min after last disconnect
         volumeMounts:
-        - name: minecraft-data
+        - name: local-data
           mountPath: /data
 
+      - name: copy-data-to-persistent
+        image: rsync
+        command: ["/bin/sh"]
+        # args: ["-c", "sleep infinity"]
+        args: ["/run-rsync.sh"]
+        volumeMounts:
+        - name: local-data
+          mountPath: /local-data
+        - name: minecraft-data
+          mountPath: /persistent-data
+        - name: rsync-config
+          mountPath: /run-rsync.sh
+          subPath: run-rsync.sh
+
+
       volumes:
       - name: minecraft-data
         persistentVolumeClaim:
           claimName: minecraft-data
+      - name: local-data
+        emptyDir: {}
+      - name: rsync-config
+        configMap:
+          name: rsync-config
+          defaultMode: 0777

apps/minecraft/kustomization.yaml

@@ -8,6 +8,7 @@ resources:
   - pvc.yaml
   - job.yaml
   - service.yaml
+  - rsync.configmap.yaml
   - curseforge.sealedsecret.yaml
 
 
@@ -15,3 +16,9 @@ images:
   - name: minecraft
     newName: itzg/minecraft-server
     newTag: java21
+  - name: alpine
+    newName: alpine
+    newTag: "3.21"
+  - name: rsync
+    newName: eeacms/rsync
+    newTag: "2.6"

apps/minecraft/rsync.configmap.yaml

@@ -0,0 +1,42 @@
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: rsync-config
+data:
+  run-rsync.sh: |-
+    #!/bin/sh
+    set -eu
+    echo "Starting rsync..."
+
+    no_change_count=0
+
+    while [ "$no_change_count" -lt 3 ]; do
+      # use the i flag to get per line output of each change
+      rsync_output=$(rsync -avzi --delete /local-data/ /persistent-data/)
+      # echo "$rsync_output"
+
+      # in this format rsync outputs at least 4 lines:
+      # ---
+      # sending incremental file list
+      #
+      # sent 145,483 bytes  received 717 bytes  26,581.82 bytes/sec
+      # total size is 708,682,765  speedup is 4,847.35
+      # ---
+      # even though a non-zero number of bytes is sent, no changes were made
+
+      line_count=$(echo "$rsync_output" | wc -l)
+
+      if [ "$line_count" -eq 4 ]; then
+        echo "Rsync output was: $rsync_output"
+        no_change_count=$((no_change_count + 1))
+        echo "No changes detected. Incrementing no_change_count to $no_change_count."
+      else
+        no_change_count=0
+        echo "Changes detected. Resetting no_change_count to 0."
+      fi
+
+      echo "Rsync completed. Sleeping for 10 minutes..."
+      sleep 600
+    done
+
+    echo "No changes detected for 3 consecutive runs. Exiting."