# External Catalogs

External catalogs connect your existing systems to Altertable, making them queryable alongside your [Altertable catalogs](/docs/lakehouse.md) and other data sources.

If inbound traffic is restricted, allow [Altertable's egress IP addresses](/docs/lakehouse/network.md#egress-ip-addresses) so managed Workers can reach the catalog. For network-restricted database-style catalogs, Altertable can also connect through an **SSH tunnel**. Configure the bastion host while creating the catalog, then copy the generated public key from the catalog details page into the SSH server's `authorized_keys`.

- [Postgres](/docs/lakehouse/external-catalogs/postgres.md): Add Postgres as an external catalog in Altertable for unified analytics. Query across Postgres and other sources with the federated query engine.
- [Supabase](/docs/lakehouse/external-catalogs/supabase.md): Add Supabase as an external catalog in Altertable for unified analytics using Transaction Pooler. Query and analyze data across Supabase and other sources.
- [MySQL](/docs/lakehouse/external-catalogs/mysql.md): Add MySQL as an external catalog for federated analytics. Query MySQL alongside other sources through Altertable's SQL engine.
- [MariaDB](/docs/lakehouse/external-catalogs/mariadb.md): Add MariaDB as an external catalog in Altertable for unified analytics. Query across MariaDB and other sources with federated query engine.
- [MongoDB](/docs/lakehouse/external-catalogs/mongodb.md): Add MongoDB as an external catalog in Altertable. Query Atlas or self-hosted collections as SQL tables alongside your other data sources.
- [BigQuery](/docs/lakehouse/external-catalogs/bigquery.md): Add BigQuery as an external catalog in Altertable for unified analytics. Configure service account credentials and required roles to query BigQuery data.
- [Snowflake](/docs/lakehouse/external-catalogs/snowflake.md): Add Snowflake as an external catalog in Altertable so teams can query warehouse data with lakehouse analytics.
- [Redshift](/docs/lakehouse/external-catalogs/redshift.md): Add Amazon Redshift as an external catalog in Altertable for unified analytics. Query and analyze data across Redshift and other sources with federated queries.
- [DuckDB](/docs/lakehouse/external-catalogs/duckdb.md): Connect an existing DuckDB database file from object storage as an external catalog for federated queries in Altertable.
- [Bucket Tables](/docs/lakehouse/external-catalogs/bucket-tables.md): Map files in a connected bucket to external Altertable tables and query object storage data from the lakehouse.
- [Iceberg Tables](/docs/lakehouse/external-catalogs/iceberg-tables.md): Map existing Iceberg tables in connected object storage to external tables in Altertable for unified lakehouse queries.
- [R2 Data Catalog](/docs/lakehouse/external-catalogs/r2-data-catalog.md): Connect Cloudflare R2 Data Catalog to Altertable as an Iceberg REST catalog for open, governed lakehouse analytics.
- [S3 Tables](/docs/lakehouse/external-catalogs/s3-tables.md): Connect Amazon S3 Tables to Altertable as an Iceberg REST catalog for managed, open-table lakehouse analytics.
- [AWS Glue](/docs/lakehouse/external-catalogs/aws-glue.md): Connect AWS Glue Data Catalog to Altertable so teams can query Iceberg tables through a shared lakehouse foundation.