How to transfer data to Amazon DocumentDB

I can use Fluentd to transfer data to mongoDB built on AWS EC2, but I can't transfer data to DocumentDB, which is a managed service compatible with mongoDB.

The following is the **td-agent.conf** for transferring the json file saved in **/var/log/test/bulk/** to mongoDB.

```

@type tail
path /var/log/test/bulk/*
tag bulk.*
format json
time_key time
time_format '%F %T.%N %z %Z'
pos_file /var/log/test/run/log-json.pos
read_from_head true
refresh_interval 5s

@type record_reformer
tag test.${tag_parts[-3]}.${tag_parts[-2]}

@type copy

@type forest
subtype mongo_replset

nodes hostname1:27017,hostname2:27017,hostname3:27017
replica_set rs0
database ${tag_parts[-2]}
collection ${tag_parts[-1]}
user ********
password ********
replace_dot_in_key_with __dot__

@type file
path /var/log/test/buffer-mongo/${tag_parts[-2..-1]}
chunk_limit_size 8m
queued_chunks_limit_size 64
flush_interval 1s

```

When transferring to DocumentDB, I changed the host in the conf file above to the cluster endpoint, but the following error occurred.

```
[warn]: #0 failed to flush the buffer. retry_time=0 next_retry_seconds=2021-09-14 10:26:56 +0900 chunk="5cbea78155b58ec0810e9fde94aa2355" error_class=Mongo::Error::NoServerAvailable error="No server is available matching preference: # using server_selection_timeout=30 and local_threshold=0.015"
```

Since TLS is enabled in DocumentDB, I wonder if I need to specify [rds-combined-ca-bundle.pem](https://s3.amazonaws.com/rds-downloads/rds-combined-ca-bundle.pem) to enable TLS. I think so, but I don't know how to do that. (When I tested writing to DocumentDB in Python using [the link](https://docs.aws.amazon.com/ja_jp/documentdb/latest/developerguide/connect_programmatically.html), the above error occurred when TLS was disabled.)

Is it possible to write data to DocumentDB with TLS enabled?