Docker Files for NebulaGraph Services

Following docker images will be ready in production.

• vesoft/nebula-graphd: nebula-graphd service built with Dockerfile.graphd
• vesoft/nebula-metad: nebula-metad service built with Dockerfile.metad
• vesoft/nebula-storaged: nebula-storaged service built with Dockerfile.storaged
• vesoft/nebula-tools: nebula tools built with Dockerfile.tools, including db_dump, meta_dump and db_upgrader