diff --git a/CloudronManifest.json b/CloudronManifest.json
index b80983a..f5c1d12 100644
--- a/CloudronManifest.json
+++ b/CloudronManifest.json
@@ -4,7 +4,7 @@
   "author": "Elastic and Cloudron Community",
   "description": "Elasticsearch is a distributed, open source search and analytics engine for all types of data. This package is designed for internal use only.",
   "tagline": "Distributed search and analytics engine",
-  "version": "1.0.14",
+  "version": "1.0.17",
   "healthCheckPath": "/_cluster/health?pretty",
   "httpPort": 9200,
   "manifestVersion": 2,
diff --git a/README.md b/README.md
index bfe8608..a30a30a 100644
--- a/README.md
+++ b/README.md
@@ -93,10 +93,17 @@ Look for `analysis-icu` in the output before running `occ fulltextsearch:index`.
 
 The package automatically configures Elasticsearch based on the container's available resources:
 
-- Java heap size is set to 50% of available memory
+- Java heap size defaults to 50% of the app's memory allocation
 - GC optimization for container environments
 - Index settings tuned for single-node operation
 
+You can override the automatic heap sizing when necessary:
+
+- Define `ES_JAVA_HEAP` (e.g. `export ES_JAVA_HEAP=8g`) in `/app/data/.env`
+- Provide a full `ES_JAVA_OPTS` string in `/app/data/.env` to take complete control
+- Add explicit `-Xms`/`-Xmx` entries in `/app/data/config/jvm.options.d/heap.options`
+- Set `ES_SKIP_AUTO_HEAP=1` in `/app/data/.env` to rely solely on the configuration files
+
 ## Limitations
 
 - This package is for internal use only and is not exposed to the web by default
diff --git a/start.sh b/start.sh
index fa24b83..2b1c8e8 100644
--- a/start.sh
+++ b/start.sh
@@ -380,20 +380,109 @@ ensure_setting() {
     fi
 }
 
+default_gc_opts() {
+    echo "-XX:+UseG1GC -XX:G1ReservePercent=25 -XX:InitiatingHeapOccupancyPercent=30 -Xlog:gc*,gc+age=trace,safepoint:file=/app/data/logs/gc/gc.log:utctime,level,pid,tags:filecount=32,filesize=64m"
+}
+
+normalize_heap_value() {
+    local raw="${1:-}"
+    raw=$(echo "$raw" | tr '[:upper:]' '[:lower:]')
+    
+    if [[ "$raw" =~ ^[0-9]+[mg]$ ]]; then
+        echo "$raw"
+        return 0
+    fi
+    
+    if [[ "$raw" =~ ^[0-9]+$ ]]; then
+        echo "${raw}m"
+        return 0
+    fi
+    
+    return 1
+}
+
+detect_memory_limit_bytes() {
+    local limit=""
+    
+    if [ -r /sys/fs/cgroup/memory.max ]; then
+        limit=$(cat /sys/fs/cgroup/memory.max)
+        if [ "$limit" != "max" ]; then
+            echo "$limit"
+            return 0
+        fi
+    fi
+    
+    if [ -r /sys/fs/cgroup/memory/memory.limit_in_bytes ]; then
+        limit=$(cat /sys/fs/cgroup/memory/memory.limit_in_bytes)
+        echo "$limit"
+        return 0
+    fi
+    
+    if [ -n "${CLOUDRON_MEMORY_LIMIT:-}" ]; then
+        # CLOUDRON_MEMORY_LIMIT is in MB
+        echo $((CLOUDRON_MEMORY_LIMIT * 1024 * 1024))
+        return 0
+    fi
+    
+    echo ""
+}
+
+has_custom_heap_file() {
+    local heap_file="$ES_PATH_CONF/jvm.options.d/heap.options"
+    if [ -f "$heap_file" ] && grep -Eq '^-Xms|^-Xmx' "$heap_file"; then
+        return 0
+    fi
+    return 1
+}
+
 # Configure JVM heap size
 configure_heap() {
-    # Calculate optimal heap size (50% of available memory)
-    CONTAINER_MEM=$(cat /sys/fs/cgroup/memory.max 2>/dev/null || echo "4294967296")
-    [ "$CONTAINER_MEM" = "max" ] && CONTAINER_MEM="4294967296"  # Default to 4GB if unlimited
+    if [ "${ES_SKIP_AUTO_HEAP:-0}" = "1" ]; then
+        echo "Skipping automatic heap sizing because ES_SKIP_AUTO_HEAP=1"
+        return 0
+    fi
     
-    HEAP_SIZE=$(expr $CONTAINER_MEM / 2097152)  # Convert to MB and take 50%
-    [ $HEAP_SIZE -gt 31744 ] && HEAP_SIZE=31744  # Max 31GB
-    [ $HEAP_SIZE -lt 512 ] && HEAP_SIZE=512      # Min 512MB
+    if [ -n "${ES_JAVA_OPTS:-}" ]; then
+        echo "Detected user-specified ES_JAVA_OPTS; not overriding heap settings."
+        return 0
+    fi
     
-    # Set JVM options
-    export ES_JAVA_OPTS="-Xms${HEAP_SIZE}m -Xmx${HEAP_SIZE}m -XX:+UseG1GC -XX:G1ReservePercent=25 -XX:InitiatingHeapOccupancyPercent=30"
-    export ES_JAVA_OPTS="$ES_JAVA_OPTS -Xlog:gc*,gc+age=trace,safepoint:file=/app/data/logs/gc/gc.log:utctime,level,pid,tags:filecount=32,filesize=64m"
+    if has_custom_heap_file; then
+        echo "Detected custom heap options in jvm.options.d; not overriding heap settings."
+        return 0
+    fi
     
+    local heap_value=""
+    
+    if [ -n "${ES_JAVA_HEAP:-}" ]; then
+        if heap_value=$(normalize_heap_value "$ES_JAVA_HEAP"); then
+            echo "Using heap size from ES_JAVA_HEAP (${heap_value})."
+        else
+            echo "Warning: ES_JAVA_HEAP value '$ES_JAVA_HEAP' is invalid; falling back to automatic sizing."
+            heap_value=""
+        fi
+    fi
+    
+    if [ -z "$heap_value" ]; then
+        local limit_bytes
+        limit_bytes=$(detect_memory_limit_bytes)
+        if [ -z "$limit_bytes" ] || [ "$limit_bytes" = "0" ]; then
+            limit_bytes=$((4 * 1024 * 1024 * 1024))
+        fi
+        
+        # Treat huge values as "unlimited" and fall back to 4GB to avoid 31GB default
+        if [ "$limit_bytes" -gt $((256 * 1024 * 1024 * 1024)) ]; then
+            limit_bytes=$((4 * 1024 * 1024 * 1024))
+        fi
+        
+        local heap_mb=$((limit_bytes / 1024 / 1024 / 2))
+        [ "$heap_mb" -gt 31744 ] && heap_mb=31744
+        [ "$heap_mb" -lt 512 ] && heap_mb=512
+        heap_value="${heap_mb}m"
+        echo "Auto-configured heap size to ${heap_value} based on container limit."
+    fi
+    
+    export ES_JAVA_OPTS="-Xms${heap_value} -Xmx${heap_value} $(default_gc_opts)"
     export PATH=$ES_HOME/bin:$PATH
 }