如何使用docker-solrs图像扩展机制创建solr核心？

我想创建一个solr的docker镜像,在启动时创建一个核心.因此我使用的是针对solr docker容器描述的docker-entrypoint-initdb.d extension mechanism.文件说

The third way of creating a core at startup is to use the image
extension mechanism explained in the next section.

但它并没有解释如何实现这一目标.

我正在使用的Dockerfile是：

FROM solr:6.6

USER root

RUN mkdir /A12Core && chown -R solr:solr /A12Core

COPY --chown=solr:solr ./services-core/search/A12Core /A12Core/
COPY --chown=solr:solr ./create-a12core.sh /docker-entrypoint-initdb.d/

USER solr

RUN chmod -R a+X /A12Core

文件夹A12Core包含核心的solr配置文件.创建核心的脚本create-a12core.sh是：

#!/bin/bash

solr-precreate A12Core /A12Core

/ A12Core目录包含以下文件：

./core.properties
./conf
./conf/update-script.js
./conf/mapping-ISOLatin1Accent.txt
./conf/schema.xml
./conf/spellings.txt
./conf/solrconfig.xml
./conf/currency.xml
./conf/mapping-FoldToASCII.txt
./conf/_schema_analysis_stopwords_english.json
./conf/stopwords.txt
./conf/synonyms.txt
./conf/elevate.xml
./conf/lang
./conf/lang/stopwords_en.txt
./conf/lang/stopwords_de.txt

但是,当使用上面的Dockerfile和脚本启动图像构建时,似乎会创建一个无限循环.输出是：

/opt/docker-solr/scripts/solr-foreground: running /docker-entrypoint-initdb.d/create-a12core.sh
Executing /opt/docker-solr/scripts/solr-precreate A12Core /A12Core
/opt/docker-solr/scripts/solr-precreate: running /docker-entrypoint-initdb.d/create-a12core.sh
Executing /opt/docker-solr/scripts/solr-precreate A12Core /A12Core
/opt/docker-solr/scripts/solr-precreate: running /docker-entrypoint-initdb.d/create-a12core.sh
Executing /opt/docker-solr/scripts/solr-precreate A12Core /A12Core
/opt/docker-solr/scripts/solr-precreate: running /docker-entrypoint-initdb.d/create-a12core.sh
...

如何使用docker-entrypoint-initdb.d扩展机制创建核心？