Detection of Instance Type is incorrect for Postgres 18

[romainrey]

Bug Description

I tried to use the proxy with a cloud sql instance using Postgres 18. It seems like the proxy is detecting it as a MySQL instance trying to connect on 3337, making it unusable.

2025/10/27 07:12:52 proxy server error: dial error: failed to dial (connection name = "#########"): dial tcp ########:3307: connect: connection refused

It should be compatible with the versions offered in cloud sql, especially given that we can't rollback an upgrade in CLoud SQL.

Thank you

Example code (or command)

// paste your code or command here

Stacktrace

Steps to reproduce?

1. ?
2. ?
3. ?
   ...

Environment

1. OS type and version:
2. Cloud SQL Proxy version (./cloud-sql-proxy --version):
3. Proxy invocation command (for example, ./cloud-sql-proxy --port 5432 INSTANCE_CONNECTION_NAME):

Additional Details

No response

[kgala2]

Hello @romainrey,

Thank you for reporting this issue. To help us diagnose the problem, could you please run the proxy command with the --debug-logs flag and share the output? This will provide us with more detailed information about the connection attempt.

Thank you

[andrii-kravets-x]

We are also impacted.

Postgres version:

POSTGRES_18_3.R20260319.00_02

I observe same error with cloud-sql-proxy versions:

v2.20.0 
v2.21.2

Command

cloud_sql_proxy REDACTED --auto-iam-authn --psc --run-connection-test --port 5432 --debug-logs

Logs

2026/04/01 19:42:55 Authorizing with Application Default Credentials
2026/04/01 19:42:55 Authorizing with Application Default Credentials
2026/04/01 19:42:55 [REDACTED] Connection info added to cache
2026/04/01 19:42:55 [REDACTED] Connection info added to cache
2026/04/01 19:42:55 [REDACTED] Connection info refresh operation started
2026/04/01 19:42:55 [REDACTED] Connection info refresh operation started
2026/04/01 19:42:55 [REDACTED] Listening on 127.0.0.1:5432
2026/04/01 19:42:55 [REDACTED] Listening on 127.0.0.1:5432
2026/04/01 19:42:55 The proxy has started successfully and is ready for new connections!
2026/04/01 19:42:55 The proxy has started successfully and is ready for new connections!
2026/04/01 19:42:55 Connection test started
2026/04/01 19:42:55 Connection test started
2026/04/01 19:42:56 [REDACTED] Connection info refresh operation complete
2026/04/01 19:42:56 [REDACTED] Current certificate expiration = 2026-04-01T20:40:01Z
2026/04/01 19:42:56 [REDACTED] Connection info refresh operation scheduled at 2026-04-01T20:36:01Z (now + 53m0s)
2026/04/01 19:42:56 [REDACTED] Now = 2026-04-01T19:42:56Z, Current cert expiration = 2026-04-01T20:40:01Z
2026/04/01 19:42:56 [REDACTED] Cert is valid = true
2026/04/01 19:42:56 [REDACTED] Dialing REDACTED.REDACTED.europe-west4.sql.goog.:3307
2026/04/01 19:42:56 [REDACTED] Connection info refresh operation complete
2026/04/01 19:42:56 [REDACTED] Current certificate expiration = 2026-04-01T20:40:01Z
2026/04/01 19:42:56 [REDACTED] Connection info refresh operation scheduled at 2026-04-01T20:36:01Z (now + 53m0s)
2026/04/01 19:42:56 [REDACTED] Now = 2026-04-01T19:42:56Z, Current cert expiration = 2026-04-01T20:40:01Z
2026/04/01 19:42:56 [REDACTED] Cert is valid = true
2026/04/01 19:42:56 [REDACTED] Dialing REDACTED.REDACTED.europe-west4.sql.goog.:3307
2026/04/01 19:45:12 [REDACTED] Dialing REDACTED.REDACTED.europe-west4.sql.goog.:3307 failed: dial tcp 10.1.0.90:3307: connect: connection timed out
2026/04/01 19:45:12 [REDACTED] Dialing REDACTED.REDACTED.europe-west4.sql.goog.:3307 failed: dial tcp 10.1.0.90:3307: connect: connection timed out
2026/04/01 19:45:12 [REDACTED] Connection info refresh operation started
2026/04/01 19:45:12 Connection test failed
2026/04/01 19:45:12 [REDACTED] Connection info refresh operation started
2026/04/01 19:45:12 Connection test failed
2026/04/01 19:45:12 proxy server error: dial error: failed to dial (connection name = "REDACTED"): dial tcp 10.1.0.90:3307: connect: connection timed out
2026/04/01 19:45:12 The proxy has encountered a terminal error: dial error: failed to dial (connection name = "REDACTED"): dial tcp 10.1.0.90:3307: connect: connection timed out
2026/04/01 19:45:12 proxy server error: dial error: failed to dial (connection name = "REDACTED"): dial tcp 10.1.0.90:3307: connect: connection timed out
2026/04/01 19:45:12 The proxy has encountered a terminal error: dial error: failed to dial (connection name = "REDACTED"): dial tcp 10.1.0.90:3307: connect: connection timed out
psql: error: connection to server at "127.0.0.1", port 5432 failed: server closed the connection unexpectedly
psql: error: connection to server at "127.0.0.1", port 5432 failed: server closed the connection unexpectedly
	This probably means the server terminated abnormally
#011This probably means the server terminated abnormally
	before or while processing the request.
#011before or while processing the request.