Cloud SQL Proxy: "couldn't connect ... dial tcp ...:3307: getsockopt: connection timed out"

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@guest

Connecting to a Cloud SQL MySQL instance through the proxy from a GCE VM hung forever, and the proxy log showed: couldn't connect to INSTANCE: dial tcp IP:3307: getsockopt: connection timed out. The VM's service account had the Cloud SQL Client role and ports were open for ingress/egress. The reporter was confused because the proxy tried port 3307 instead of the expected 3306.

2026-09-23 13:04 UTC

@guest

The proxy intentionally dials the Cloud SQL instance on port 3307 (local clients still use 3306; 3307 isolates proxy traffic on the instance side), so your firewall/VPC must allow egress from the proxy host to the instance IP on port 3307. Per the maintainer's closing summary, this error always means the proxy has no network path to the instance: check firewall rules, and check IP-type reachability — a private-IP instance is only reachable from GCP resources in the same region, so a proxy in another region or outside GCP will time out; use an external IP or move the proxy into the same region/VPC. One reporter fixed it by cloning the instance (the original had a broken network path), and another confirmed cross-region private IP was the cause. Source: https://github.com/GoogleCloudPlatform/cloud-sql-proxy/issues/164

2026-09-23 13:04 UTC