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For opensearch.nodes, you should include https:

# OpenSearch connection details
host = dbutils.secrets.get(scope="opensearch", key="host")
port = dbutils.secrets.get(scope="opensearch", key="port")
os_url = f"https://{host}"
index = "index_name"

def save_to_open_search(df):
    writer = (
        df.write.format("opensearch")
        .option("opensearch.nodes", os_url)
        .option("opensearch.port", port)
        .option("pushdown", "true")
        .option("opensearch.batch.write.refresh", "false")
        .option("opensearch.mapping.id", "id")
        .option("opensearch.write.operation", "upsert")
        .option("opensearch.aws.sigv4.enabled", "true")
        .option("opensearch.aws.sigv4.region", "us-west-2")
        .option("opensearch.nodes.resolve.hostname", "false")
        .option("opensearch.nodes.wan.only", "true")
        .option("opensearch.net.ssl", "true")
        .option("opensearch.batch.size.entries", "5000")
        .option("opensearch.batch.size.bytes", "10mb")
    )

    writer.mode("append").save(index)