如何在Docker中配置JanusGraph与Apache Cassandra？

问题描述 #

在Docker容器环境下，如何配置Apache Cassandra以与JanusGraph协同工作？需要搭建一个外部JanusGraph来处理千万级别的数据记录，本人是Cassandra、JanusGraph及图数据库领域的新手。

已执行操作步骤 #

• 下载并安装Docker程序
• 创建并启动JanusGraph Docker容器

docker run -d -p 8182:8182 janusgraph/janusgraph

• 创建并启动Apache Cassandra Docker容器

docker run --name jg-cassandra -d -e CASSANDRA_START_RPC=true -p 9160:9160 
   -p 9042:9042 -p 7199:7199 -p 7001:7001 -p 7000:7000 cassandra:3.11

• 编写并运行测试代码，尝试让JanusGraph实例连接Cassandra容器

JanusGraph janusGraph = JanusGraphFactory.build().set("storage.backend", "cql").set("storage.hostname", "localhost:9042").open();

执行结果 #

• 预期：JanusGraphFactory实例成功连接Cassandra Docker容器
• 实际：连接失败，抛出错误

错误信息：

java.lang.Throwable: Hook creation trace
    at org.janusgraph.graphdb.database.StandardJanusGraph.<init>(StandardJanusGraph.java:250) [janusgraph-core-1.0.0-20230424-065649.dcd3240.jar:?]
    at org.janusgraph.core.JanusGraphFactory.open(JanusGraphFactory.java:176) [janusgraph-core-1.0.0-20230424-065649.dcd3240.jar:?]
    at org.janusgraph.core.JanusGraphFactory.open(JanusGraphFactory.java:147) [janusgraph-core-1.0.0-20230424-065649.dcd3240.jar:?]
    at org.janusgraph.core.JanusGraphFactory.open(JanusGraphFactory.java:137) [janusgraph-core-1.0.0-20230424-065649.dcd3240.jar:?]
    at org.janusgraph.core.JanusGraphFactory$Builder.open(JanusGraphFactory.java:277) [janusgraph-core-1.0.0-20230424-065649.dcd3240.jar:?]
    at Main.main(Main.java:10) [classes/:?]

测试代码Main.java：

// Main
import org.janusgraph.core.JanusGraph;
import org.janusgraph.core.JanusGraphFactory;

public class Main {
    public static void main(String[] args) {
        JanusGraph janusGraph = JanusGraphFactory.build().set("storage.backend", "cql").set("storage.hostname", "localhost:9042").open();
        janusGraph.close();
    }
}

依赖配置pom.xml：

<!-- pom.xml -->
    <dependencies>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-slf4j2-impl</artifactId>
            <version>2.20.0</version>
        </dependency>
        <dependency>
            <groupId>org.janusgraph</groupId>
            <artifactId>janusgraph-core</artifactId>
            <version>1.0.0-20230424-065649.dcd3240</version>
        </dependency>
        <dependency>
            <groupId>org.apache.tinkerpop</groupId>
            <artifactId>gremlin-core</artifactId>
            <version>3.6.2</version>
        </dependency>
        <dependency>
            <groupId>org.janusgraph</groupId>
            <artifactId>janusgraph-cql</artifactId>
            <version>1.0.0-20230428-082704.5159135</version>
        </dependency>
    </dependencies>

问题排查与解决思路 #

1. 统一JanusGraph组件版本 #

你的janusgraph-core与janusgraph-cql版本不匹配，这是引发兼容性错误的核心原因。JanusGraph核心模块与存储适配模块必须使用完全一致的版本，修改pom.xml中的版本配置：

<dependency>
    <groupId>org.janusgraph</groupId>
    <artifactId>janusgraph-core</artifactId>
    <version>1.0.0-20230428-082704.5159135</version>
</dependency>
<dependency>
    <groupId>org.janusgraph</groupId>
    <artifactId>janusgraph-cql</artifactId>
    <version>1.0.0-20230428-082704.5159135</version>
</dependency>

2. 验证Cassandra容器状态 #

启动Cassandra容器后需要等待1-2分钟完成初始化，可通过以下命令确认容器是否就绪：

docker exec jg-cassandra nodetool status

输出中节点状态显示UN（Up/Normal），说明Cassandra已正常运行。

3. 优化JanusGraph连接配置 #

连接参数不需要在storage.hostname中携带端口（默认使用9042），可补充指定keyspace参数确保配置完整：

JanusGraph janusGraph = JanusGraphFactory.build()
    .set("storage.backend", "cql")
    .set("storage.hostname", "localhost")
    .set("storage.cql.keyspace", "janusgraph")
    .open();

4. 清理无用JanusGraph容器 #

你启动的janusgraph/janusgraph默认自带嵌入式存储，若仅需连接外部Cassandra，可停止并删除该容器以节省资源：

docker stop $(docker ps -q --filter ancestor=janusgraph/janusgraph)
docker rm $(docker ps -aq --filter ancestor=janusgraph/janusgraph)

内容的提问来源于stack exchange，提问作者Zach