最近我发现了fly.io作为Heroku的替代品，他们从11月28日起停止提供免费的dynos。有一个关于如何使用Deno-mit fly.io和Buildpacks的指南，但不适用于Spring Boot/Java。
此外，我还阅读了文档中fly.toml中的build部分。他们声明定义builder和buildpacks，如下所示：
[build]
builder = "paketobuildpacks/builder:base"
buildpacks = ["gcr.io/paketo-buildpacks/nodejs"]
因此，对于Spring Boot，我在以下配置中采用了这一点：
[build]
builder = "paketobuildpacks/builder:base"
buildpacks = ["gcr.io/paketo-buildpacks/spring-boot"]
但当我运行fly deploy时，构建器被正确加载，但在DETECTING阶段内，我遇到了以下错误：
$ 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
作为Cloud Native Buildpacks(CNB(的普通用户，fly.io文档声明定义buildpacks参数，我觉得很奇怪。由于CNB的众多好处之一是，它们可以检测您的应用程序需要什么才能构建。包括所有需要的构建包。因此，只有定义构建器，然后检测所需的构建包，才有意义。
这也是解决方案。您只需在build配置中省略buildpacks设置即可。builder标签就是我们所需要的：
[build]
builder = "paketobuildpacks/builder:base"
这将正确激活您项目的Buildpacks检测，并触发fly.io上的成功部署。它还将直接将映像推送到位于registry.fly.io/microservice-api-spring-boot的fly.io Docker注册表。以下是fly deploy:的输出示例
$ 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
Digest: sha256:bbc26d8b7fe183a1d59fba3e19b55d7a1e647de0bbf5aa14be98e328c4b7d777
Status: Image is up to date for paketobuildpacks/builder:base
base-cnb: Pulling from paketobuildpacks/run
Digest: sha256:cfc9b596bedc7bead1b3714a69dffa1fb17fcb1f7bba5c3faadb40c0b6f5acbd
Status: Image is up to date for paketobuildpacks/run:base-cnb
===> DETECTING
10 of 24 buildpacks participating
paketo-buildpacks/ca-certificates 3.3.0
paketo-buildpacks/bellsoft-liberica 9.6.1
paketo-buildpacks/syft 1.18.0
paketo-buildpacks/maven 6.7.0
paketo-buildpacks/executable-jar 6.4.0
paketo-buildpacks/apache-tomcat 7.5.0
paketo-buildpacks/apache-tomee 1.2.0
paketo-buildpacks/liberty 2.1.1
paketo-buildpacks/dist-zip 5.3.0
paketo-buildpacks/spring-boot 5.18.0
===> ANALYZING
Previous image with name "registry.fly.io/microservice-api-spring-boot:cache" not found
===> RESTORING
===> BUILDING
Paketo CA Certificates Buildpack 3.3.0
https://github.com/paketo-buildpacks/ca-certificates
Launch Helper: Contributing to layer
Creating /layers/paketo-buildpacks_ca-certificates/helper/exec.d/ca-certificates-helper
Paketo BellSoft Liberica Buildpack 9.6.1
https://github.com/paketo-buildpacks/bellsoft-liberica
Build Configuration:
$BP_JVM_JLINK_ARGS --no-man-pages --no-header-files --strip-debug --compress=1 configure custom link arguments (--output must be omitted)
$BP_JVM_JLINK_ENABLED false enables running jlink tool to generate custom JRE
$BP_JVM_TYPE JRE the JVM type - JDK or JRE
$BP_JVM_VERSION 11 the Java version
Launch Configuration:
$BPL_DEBUG_ENABLED false enables Java remote debugging support
$BPL_DEBUG_PORT 8000 configure the remote debugging port
$BPL_DEBUG_SUSPEND false configure whether to suspend execution until a debugger has attached
$BPL_HEAP_DUMP_PATH write heap dumps on error to this path
$BPL_JAVA_NMT_ENABLED true enables Java Native Memory Tracking (NMT)
$BPL_JAVA_NMT_LEVEL summary configure level of NMT, summary or detail
$BPL_JFR_ARGS configure custom Java Flight Recording (JFR) arguments
$BPL_JFR_ENABLED false enables Java Flight Recording (JFR)
$BPL_JMX_ENABLED false enables Java Management Extensions (JMX)
$BPL_JMX_PORT 5000 configure the JMX port
$BPL_JVM_HEAD_ROOM 0 the headroom in memory calculation
$BPL_JVM_LOADED_CLASS_COUNT 35% of classes the number of loaded classes in memory calculation
$BPL_JVM_THREAD_COUNT 250 the number of threads in memory calculation
$JAVA_TOOL_OPTIONS the JVM launch flags
Using buildpack default Java version 11
BellSoft Liberica JDK 11.0.16: Contributing to layer
Downloading from https://github.com/bell-sw/Liberica/releases/download/11.0.16.1+1/bellsoft-jdk11.0.16.1+1-linux-amd64.tar.gz
Verifying checksum
Expanding to /layers/paketo-buildpacks_bellsoft-liberica/jdk
Adding 127 container CA certificates to JVM truststore
Writing env.build/JAVA_HOME.override
Writing env.build/JDK_HOME.override
BellSoft Liberica JRE 11.0.16: Contributing to layer
Downloading from https://github.com/bell-sw/Liberica/releases/download/11.0.16.1+1/bellsoft-jre11.0.16.1+1-linux-amd64.tar.gz
Verifying checksum
Expanding to /layers/paketo-buildpacks_bellsoft-liberica/jre
Adding 127 container CA certificates to JVM truststore
Writing env.launch/BPI_APPLICATION_PATH.default
Writing env.launch/BPI_JVM_CACERTS.default
Writing env.launch/BPI_JVM_CLASS_COUNT.default
Writing env.launch/BPI_JVM_SECURITY_PROVIDERS.default
Writing env.launch/JAVA_HOME.default
Writing env.launch/JAVA_TOOL_OPTIONS.append
Writing env.launch/JAVA_TOOL_OPTIONS.delim
Writing env.launch/MALLOC_ARENA_MAX.default
Launch Helper: Contributing to layer
Creating /layers/paketo-buildpacks_bellsoft-liberica/helper/exec.d/active-processor-count
Creating /layers/paketo-buildpacks_bellsoft-liberica/helper/exec.d/java-opts
Creating /layers/paketo-buildpacks_bellsoft-liberica/helper/exec.d/jvm-heap
Creating /layers/paketo-buildpacks_bellsoft-liberica/helper/exec.d/link-local-dns
Creating /layers/paketo-buildpacks_bellsoft-liberica/helper/exec.d/memory-calculator
Creating /layers/paketo-buildpacks_bellsoft-liberica/helper/exec.d/security-providers-configurer
Creating /layers/paketo-buildpacks_bellsoft-liberica/helper/exec.d/jmx
Creating /layers/paketo-buildpacks_bellsoft-liberica/helper/exec.d/jfr
Creating /layers/paketo-buildpacks_bellsoft-liberica/helper/exec.d/security-providers-classpath-9
Creating /layers/paketo-buildpacks_bellsoft-liberica/helper/exec.d/debug-9
Creating /layers/paketo-buildpacks_bellsoft-liberica/helper/exec.d/nmt
Creating /layers/paketo-buildpacks_bellsoft-liberica/helper/exec.d/openssl-certificate-loader
Java Security Properties: Contributing to layer
Writing env.launch/JAVA_SECURITY_PROPERTIES.default
Writing env.launch/JAVA_TOOL_OPTIONS.append
Writing env.launch/JAVA_TOOL_OPTIONS.delim
Paketo Buildpack for Syft 1.18.0
https://github.com/paketo-buildpacks/syft
Downloading from https://github.com/anchore/syft/releases/download/v0.55.0/syft_0.55.0_linux_amd64.tar.gz
Verifying checksum
Writing env.build/SYFT_CHECK_FOR_APP_UPDATE.default
Paketo Maven Buildpack 6.7.0
https://github.com/paketo-buildpacks/maven
Build Configuration:
$BP_MAVEN_BUILD_ARGUMENTS -Dmaven.test.skip=true --no-transfer-progress package the arguments to pass to Maven
$BP_MAVEN_BUILT_ARTIFACT target/*.[ejw]ar the built application artifact explicitly. Supersedes $BP_MAVEN_BUILT_MODULE
$BP_MAVEN_BUILT_MODULE the module to find application artifact in
$BP_MAVEN_DAEMON_ENABLED false use maven daemon
$BP_MAVEN_POM_FILE pom.xml the location of the main pom.xml file, relative to the application root
$BP_MAVEN_SETTINGS_PATH the path to a Maven settings file
Apache Maven 3.8.6: Contributing to layer
Downloading from https://repo1.maven.org/maven2/org/apache/maven/apache-maven/3.8.6/apache-maven-3.8.6-bin.tar.gz
Verifying checksum
Expanding to /layers/paketo-buildpacks_maven/maven
Creating cache directory /home/cnb/.m2
Compiled Application: Contributing to layer
Executing mvn --batch-mode -Dmaven.test.skip=true --no-transfer-progress package
[INFO] Scanning for projects...
[INFO]
[INFO] -------< org.springframework.boot:microservice-api-spring-boot >--------
[INFO] Building microservice-api-spring-boot 2.7.2
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-resources-plugin:3.2.0:resources (default-resources) @ microservice-api-spring-boot ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Using 'UTF-8' encoding to copy filtered properties files.
[INFO] Copying 1 resource
[INFO] Copying 0 resource
[INFO]
[INFO] --- maven-compiler-plugin:3.10.1:compile (default-compile) @ microservice-api-spring-boot ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 6 source files to /workspace/target/classes
[INFO] /workspace/src/main/java/de/jonashackt/springbootvuejs/configuration/WebSecurityConfiguration.java: /workspace/src/main/java/de/jonashackt/springbootvuejs/configuration/WebSecurityConfiguration.java uses or overrides a deprecated API.
[INFO] /workspace/src/main/java/de/jonashackt/springbootvuejs/configuration/WebSecurityConfiguration.java: Recompile with -Xlint:deprecation for details.
[INFO]
[INFO] --- maven-resources-plugin:3.2.0:testResources (default-testResources) @ microservice-api-spring-boot ---
[INFO] Not copying test resources
[INFO]
[INFO] --- maven-compiler-plugin:3.10.1:testCompile (default-testCompile) @ microservice-api-spring-boot ---
[INFO] Not compiling test sources
[INFO]
[INFO] --- maven-surefire-plugin:2.22.2:test (default-test) @ microservice-api-spring-boot ---
[INFO] Tests are skipped.
[INFO]
[INFO] --- maven-jar-plugin:3.2.2:jar (default-jar) @ microservice-api-spring-boot ---
[INFO] Building jar: /workspace/target/microservice-api-spring-boot-2.7.2.jar
[INFO]
[INFO] --- spring-boot-maven-plugin:2.7.2:repackage (repackage) @ microservice-api-spring-boot ---
[INFO] Replacing main artifact with repackaged archive
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 10.274 s
[INFO] Finished at: 2022-09-12T10:49:04Z
[INFO] ------------------------------------------------------------------------
Removing source code
Restoring application artifact
Paketo Executable JAR Buildpack 6.4.0
https://github.com/paketo-buildpacks/executable-jar
Class Path: Contributing to layer
Writing env/CLASSPATH.delim
Writing env/CLASSPATH.prepend
Process types:
executable-jar: java org.springframework.boot.loader.JarLauncher (direct)
task: java org.springframework.boot.loader.JarLauncher (direct)
web: java org.springframework.boot.loader.JarLauncher (direct)
Paketo Buildpack for Spring Boot 5.18.0
https://github.com/paketo-buildpacks/spring-boot
Build Configuration:
$BP_SPRING_CLOUD_BINDINGS_DISABLED false whether to contribute Spring Boot cloud bindings support
Launch Configuration:
$BPL_SPRING_CLOUD_BINDINGS_DISABLED false whether to auto-configure Spring Boot environment properties from bindings
$BPL_SPRING_CLOUD_BINDINGS_ENABLED true Deprecated - whether to auto-configure Spring Boot environment properties from bindings
Creating slices from layers index
dependencies (50.6 MB)
spring-boot-loader (283.6 KB)
snapshot-dependencies (0.0 B)
application (71.5 KB)
Launch Helper: Contributing to layer
Creating /layers/paketo-buildpacks_spring-boot/helper/exec.d/spring-cloud-bindings
Spring Cloud Bindings 1.10.0: Contributing to layer
Downloading from https://repo.spring.io/release/org/springframework/cloud/spring-cloud-bindings/1.10.0/spring-cloud-bindings-1.10.0.jar
Verifying checksum
Copying to /layers/paketo-buildpacks_spring-boot/spring-cloud-bindings
Web Application Type: Contributing to layer
Servlet web application detected
Writing env.launch/BPL_JVM_THREAD_COUNT.default
4 application slices
Image labels:
org.opencontainers.image.title
org.opencontainers.image.version
org.springframework.boot.version
===> EXPORTING
Adding layer 'paketo-buildpacks/ca-certificates:helper'
Adding layer 'paketo-buildpacks/bellsoft-liberica:helper'
Adding layer 'paketo-buildpacks/bellsoft-liberica:java-security-properties'
Adding layer 'paketo-buildpacks/bellsoft-liberica:jre'
Adding layer 'paketo-buildpacks/executable-jar:classpath'
Adding layer 'paketo-buildpacks/spring-boot:helper'
Adding layer 'paketo-buildpacks/spring-boot:spring-cloud-bindings'
Adding layer 'paketo-buildpacks/spring-boot:web-application-type'
Adding 5/5 app layer(s)
Adding layer 'launcher'
Adding layer 'config'
Adding layer 'process-types'
Adding label 'io.buildpacks.lifecycle.metadata'
Adding label 'io.buildpacks.build.metadata'
Adding label 'io.buildpacks.project.metadata'
Adding label 'org.opencontainers.image.title'
Adding label 'org.opencontainers.image.version'
Adding label 'org.springframework.boot.version'
Setting default process type 'web'
Saving registry.fly.io/microservice-api-spring-boot:cache...
*** Images (28a69cfce36e):
registry.fly.io/microservice-api-spring-boot:cache
registry.fly.io/microservice-api-spring-boot:deployment-01GCRMZ79R99H9RRXFK7H47X3B
Adding cache layer 'paketo-buildpacks/bellsoft-liberica:jdk'
Adding cache layer 'paketo-buildpacks/syft:syft'
Adding cache layer 'paketo-buildpacks/maven:application'
Adding cache layer 'paketo-buildpacks/maven:cache'
Adding cache layer 'paketo-buildpacks/maven:maven'
--> Building image done
==> Pushing image to fly
The push refers to repository [registry.fly.io/microservice-api-spring-boot]
1dc94a70dbaa: Pushed
...
4a641e21953d: Pushed
deployment-01GCRMZ79R99H9RRXFK7H47X3B: digest: sha256:5e77e023b3862ec1edffcee1d78c5b23a5ae6957f6028da0bff16e4b7fd5264f size: 4702
--> Pushing image done
image: registry.fly.io/microservice-api-spring-boot:deployment-01GCRMZ79R99H9RRXFK7H47X3B
image size: 296 MB
==> Creating release
--> release v4 created
--> You can detach the terminal anytime without stopping the deployment
==> Monitoring deployment
1 desired, 1 placed, 1 healthy, 0 unhealthy [health checks: 1 total, 1 passing]
--> v4 deployed successfully