Add configurable cache size limit for S3 uploads

Skip uploading build cache to S3 when it exceeds the size limit.
Configurable via APPPACK_MAX_CACHE_SIZE_GB environment variable
(default: 7GB). Set to 0 to disable the limit entirely.

Invalid or negative values fall back to the default with a warning.

Author: dmonroy

builder/build/build.go

@@ -5,6 +5,8 @@ import (
 	"io"
 	"os"
 	"os/exec"
+	"path/filepath"
+	"strconv"
 	"strings"
 	"sync"
 
@@ -17,8 +19,10 @@ import (
 )
 
 const (
-	DockerHubMirror = "registry.apppackcdn.net"
-	CacheDirectory  = "/tmp/apppack-cache"
+	DockerHubMirror       = "registry.apppackcdn.net"
+	CacheDirectory        = "/tmp/apppack-cache"
+	DefaultMaxCacheSizeGB = 7
+	MaxCacheSizeEnvVar    = "APPPACK_MAX_CACHE_SIZE_GB"
 )
 
 func stripParamPrefix(params map[string]string, prefix string, final *map[string]string) {
@@ -220,8 +224,50 @@ func (b *Build) pushImages(config *containers.BuildConfig) error {
 	return nil
 }
 
+func dirSize(path string) (int64, error) {
+	var size int64
+	err := filepath.Walk(path, func(_ string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+		if !info.IsDir() {
+			size += info.Size()
+		}
+		return nil
+	})
+	return size, err
+}
+
+func getMaxCacheSizeGB() int {
+	maxGB := DefaultMaxCacheSizeGB
+	if val := os.Getenv(MaxCacheSizeEnvVar); val != "" {
+		parsed, err := strconv.Atoi(val)
+		if err != nil {
+			fmt.Printf("WARNING: Invalid %s value '%s', using default %dGB\n", MaxCacheSizeEnvVar, val, DefaultMaxCacheSizeGB)
+		} else if parsed < 0 {
+			fmt.Printf("WARNING: Negative %s value '%d', using default %dGB\n", MaxCacheSizeEnvVar, parsed, DefaultMaxCacheSizeGB)
+		} else {
+			maxGB = parsed // 0 disables the limit
+		}
+	}
+	return maxGB
+}
+
 func (b *Build) archiveCache() error {
 	fmt.Println("Archiving build cache to S3 ...")
+	maxGB := getMaxCacheSizeGB()
+	if maxGB > 0 {
+		maxSize := int64(maxGB) * 1024 * 1024 * 1024
+		size, err := dirSize(CacheDirectory)
+		if err != nil {
+			b.Log().Warn().Err(err).Msg("failed to calculate cache directory size")
+		} else if size > maxSize {
+			sizeMB := size / (1024 * 1024)
+			fmt.Printf("WARNING: Cache directory is %dMB, exceeding %dGB limit. Skipping cache upload.\n", sizeMB, maxGB)
+			b.Log().Warn().Int64("size_bytes", size).Int("max_gb", maxGB).Msg("cache directory exceeds size limit, skipping upload")
+			return nil
+		}
+	}
 	quiet := b.Log().GetLevel() > zerolog.DebugLevel
 	return b.aws.SyncToS3(CacheDirectory, b.ArtifactBucket, "cache", quiet)
 }

builder/build/build_test.go

@@ -2,6 +2,8 @@ package build
 
 import (
 	"fmt"
+	"os"
+	"path/filepath"
 	"testing"
 )
 
@@ -94,3 +96,80 @@ func TestGenerateDockerEnvStrings(t *testing.T) {
 		t.Errorf("expected %d elements, got %d", len(expected), len(actual))
 	}
 }
+
+func TestGetMaxCacheSizeGB(t *testing.T) {
+	tests := []struct {
+		name     string
+		envValue string
+		want     int
+	}{
+		{"unset uses default", "", DefaultMaxCacheSizeGB},
+		{"valid value", "10", 10},
+		{"zero disables limit", "0", 0},
+		{"invalid string falls back to default", "abc", DefaultMaxCacheSizeGB},
+		{"negative falls back to default", "-5", DefaultMaxCacheSizeGB},
+		{"float falls back to default", "7.5", DefaultMaxCacheSizeGB},
+		{"whitespace falls back to default", " ", DefaultMaxCacheSizeGB},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if tt.envValue == "" {
+				os.Unsetenv(MaxCacheSizeEnvVar)
+			} else {
+				os.Setenv(MaxCacheSizeEnvVar, tt.envValue)
+			}
+			defer os.Unsetenv(MaxCacheSizeEnvVar)
+
+			got := getMaxCacheSizeGB()
+			if got != tt.want {
+				t.Errorf("getMaxCacheSizeGB() = %d, want %d", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestDirSize(t *testing.T) {
+	// Create a temp directory with known file sizes
+	tmpDir, err := os.MkdirTemp("", "dirsize-test")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(tmpDir)
+
+	// Create files with known sizes
+	file1 := filepath.Join(tmpDir, "file1.txt")
+	file2 := filepath.Join(tmpDir, "file2.txt")
+	if err := os.WriteFile(file1, make([]byte, 1000), 0644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(file2, make([]byte, 500), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	// Create subdirectory with file
+	subDir := filepath.Join(tmpDir, "subdir")
+	if err := os.Mkdir(subDir, 0755); err != nil {
+		t.Fatal(err)
+	}
+	file3 := filepath.Join(subDir, "file3.txt")
+	if err := os.WriteFile(file3, make([]byte, 250), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	size, err := dirSize(tmpDir)
+	if err != nil {
+		t.Errorf("dirSize() error = %v", err)
+	}
+	expectedSize := int64(1750)
+	if size != expectedSize {
+		t.Errorf("dirSize() = %d, want %d", size, expectedSize)
+	}
+}
+
+func TestDirSizeNonExistent(t *testing.T) {
+	_, err := dirSize("/nonexistent/path/that/does/not/exist")
+	if err == nil {
+		t.Error("dirSize() expected error for non-existent path, got nil")
+	}
+}