Elasticsearch: groupby query error in case of default template is used

2019/06/06 16:37:38 Error during request: Invalid write response (status 400): {"error":{"root_cause":[{"type":"illegal_argument_exception","reason":"Fielddata is disabled on text fields by default. Set fielddata=true on [hostname] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory. Alternatively use a keyword field instead."}],"type":"search_phase_execution_exception","reason":"all shards failed","phase":"query","grouped":true,"failed_shards":[{"shard":0,"index":"cpu","node":"a-7hFd9DRaaejFX2MNRMjg","reason":{"type":"illegal_argument_exception","reason":"Fielddata is disabled on text fields by default. Set fielddata=true on [hostname] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory. Alternatively use a keyword field instead."}}],"caused_by":{"type":"illegal_argument_exception","reason":"Fielddata is disabled on text fields by default. Set fielddata=true on [hostname] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory. Alternatively use a keyword field instead.","caused_by":{"type":"illegal_argument_exception","reason":"Fielddata is disabled on text fields by default. Set fielddata=true on [hostname] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory. Alternatively use a keyword field instead."}}},"status":400}

Start by reproducing the groupby query with the default template and inspect the Elasticsearch mapping for the hostname field. Compare the default template with the query's grouping field and confirm the fix by rerunning the same request without the status-400 fielddata error.

Written by the indexing model from the issue text.