Unable to parse json logs

2019-07-31T14:29:12.644Z DEBUG [elasticsearch] elasticsearch/client.go:507 Bulk item insert failed (i=12, status=500): {"type":"exception","reason":"java.lang.IllegalArgumentException: java.lang.IllegalArgumentException: com.fasterxml.jackson.core.JsonParseException: Unexpected character ('f' (code 102)): was expecting double-quote to start field name\n at [Source: org.elasticsearch.common.bytes.BytesReference$MarkSupportingStreamInputWrapper@59ee9ae1; line: 1, column: 3]","caused_by":{"type":"illegal_argument_exception","reason":"java.lang.IllegalArgumentException: com.fasterxml.jackson.core.JsonParseException: Unexpected character ('f' (code 102)): was expecting double-quote to start field name\n at [Source: org.elasticsearch.common.bytes.BytesReference$MarkSupportingStreamInputWrapper@59ee9ae1; line: 1, column: 3]","caused_by":{"type":"illegal_argument_exception","reason":"com.fasterxml.jackson.core.JsonParseException: Unexpected character ('f' (code 102)): was expecting double-quote to start field name\n at [Source: org.elasticsearch.common.bytes.BytesReference$MarkSupportingStreamInputWrapper@59ee9ae1; line: 1, column: 3]","caused_by":{"type":"json_parse_exception","reason":"Unexpected character ('f' (code 102)): was expecting double-quote to start field name\n at [Source: org.elasticsearch.common.bytes.BytesReference$MarkSupportingStreamInputWrapper@59ee9ae1; line: 1, column: 3]"}}},"header":{"processor_type":"json"}}

please take the time to properly write up your problem instead of just pasting snippets. Also take the time to properly format snippets, as this forum supports markdown (and therefore nicely formatted code snippets).

it seems you tried to index invalid JSON. Can you share the data you tried to index?