在fly.io部署Spring Boot应用遇Buildpack检测错误：无构建包组通过检测

核心原因 #

Paketo的Spring Boot Buildpack无法通过检测，通常是因为缺少依赖的JDK环境，或者项目目录中没有符合要求的构建产物（可执行Jar）或构建配置文件（pom.xml/build.gradle）。

解决方案 #

1. 使用包含完整Java支持的Builder #

直接替换为包含JDK、构建工具及Spring Boot支持的full builder，无需单独指定Buildpack：

[build]
  builder = "paketobuildpacks/builder:full"

2. 补充依赖的JDK Buildpack（若坚持用base builder） #

base builder仅包含基础环境，需同时添加JDK Buildpack和Spring Boot Buildpack：

[build]
  builder = "paketobuildpacks/builder:base"
  buildpacks = ["gcr.io/paketo-buildpacks/java", "gcr.io/paketo-buildpacks/spring-boot"]

3. 确保项目构建产物或配置存在 #

• 若已本地构建项目，确认target/（Maven）或build/libs/（Gradle）目录下有可执行的Spring Boot Jar包；
• 若未本地构建，确保项目根目录存在pom.xml（Maven）或build.gradle/build.gradle.kts（Gradle），Buildpack会自动触发构建流程。

4. 确认部署上下文路径 #

执行fly deploy时，确保当前工作目录是Spring Boot项目根目录，或通过--path参数指定路径：

fly deploy --path ./your-spring-boot-project-root

问题重现 #

背景 #

Heroku自11月28日停止提供免费dyno服务，尝试用Fly.io作为替代方案部署Spring Boot项目，但Fly.io官方文档缺少Spring Boot/Java相关指南。参考Fly.io的Buildpack配置示例，适配了如下fly.toml配置：

[build]
  builder = "paketobuildpacks/builder:base"
  buildpacks = ["gcr.io/paketo-buildpacks/spring-boot"]

错误日志 #

执行fly deploy时在DETECTING阶段报错：

$ fly deploy
==> Verifying app config
--> Verified app config
==> Building image
Remote builder fly-builder-little-silence-4534 ready
==> Building image with Buildpacks
--> docker host: 20.10.12 linux x86_64
base: Pulling from paketobuildpacks/builder
b5da66d4625a: Pulling fs layer
...
4f4fb700ef54: Pull complete
Digest: sha256:bbc26d8b7fe183a1d59fba3e19b55d7a1e647de0bbf5aa14be98e328c4b7d777
Status: Downloaded newer image for paketobuildpacks/builder:base
base-cnb: Pulling from paketobuildpacks/run
b5da66d4625a: Already exists
80857de9da00: Already exists
239caa1e3c6f: Pull complete
ed65ad332a5e: Pull complete
4fe6ac7cc235: Pull complete
Digest: sha256:cfc9b596bedc7bead1b3714a69dffa1fb17fcb1f7bba5c3faadb40c0b6f5acbd
Status: Downloaded newer image for paketobuildpacks/run:base-cnb
latest: Pulling from paketo-buildpacks/spring-boot
3301de03cfeb: Pull complete
Digest: sha256:a6551c90f9af0719233ff4a97408a8ea8054e90f776b592dcbc7f37c03c9518c
Status: Downloaded newer image for gcr.io/paketo-buildpacks/spring-boot:latest
===> DETECTING
ERROR: No buildpack groups passed detection.
ERROR: Please check that you are running against the correct path.
ERROR: failed to detect: no buildpacks participating
Error failed to fetch an image or build from source: executing lifecycle: failed with status code: 20

内容的提问来源于stack exchange，提问作者jonashackt