Recently, the crawler job often fails after 10+ hours with the following
error (10.0.47.27:9200 is the ElasticSearch master):
dial tcp 10.0.47.27:9200: connect: connection refused
Currently, the `kustomize` index in ElasticSearch is using dynamic
mapping, which sets the types of all the fields to `text`. However,
`text` field type is good for full-text value matching, and not good for
exact-value matching. For exact-value matching, the `keyword` filed
type should be used.