Providing discovery systems for eresourcesis essential for library services today. Commercial search engine indices have been a widely used solution in recent years. In contrast, running an own discovery service is undoubtedly a challenging task but promises full control over data processing, enrichment, performance and quality. Building an own aggregated index of eresourcesincludes gathering the right mix of data sources, clearing licensing issues, and negotiating data availability. Technically, these threads are resumed by data harvesters, filters and workflow orchestration tools.