Failure to connect to proxy "Certificate signed by unknown authority" - go

Question

I'm attempting to connect to a CloudSQL instance via a cloudsql-proxy container on my Kubernetes deployment. I have the cloudsql credentials mounted and the value of GOOGLE_APPLICATION_CREDENTIALS set.
However, I'm still receiving the following error in my logs:
2018/10/08 20:07:28 Failed to connect to database: Post https://www.googleapis.com/sql/v1beta4/projects/[projectID]/instances/[appName]/createEphemeral?alt=json&prettyPrint=false: oauth2: cannot fetch token: Post https://oauth2.googleapis.com/token: x509: certificate signed by unknown authority
My connection string looks like this:
[dbUser]:[dbPassword]#cloudsql([instanceName])/[dbName]]?charset=utf8&parseTime=True&loc=Local
And the proxy dialer is shadow-imported as:
_ github.com/GoogleCloudPlatform/cloudsql-proxy/proxy/dialers/mysql
Anyone have an idea what might be missing?
EDIT:
Deployment Spec looks something like this (JSON formatted):
{
"replicas": 1,
"selector": {
...
},
"template": {
...
"spec": {
"containers": [
{
"image": "[app-docker-imager]",
"name": "...",
"env": [
...
{
"name": "MYSQL_PASSWORD",
...
},
{
"name": "MYSQL_USER",
...
},
{
"name": "GOOGLE_APPLICATION_CREDENTIALS",
"value": "..."
}
],
"ports": [
{
"containerPort": 8080,
"protocol": "TCP"
}
],
"volumeMounts": [
{
"mountPath": "/secrets/cloudsql",
"name": "[secrets-mount-name]",
"readOnly": true
}
]
},
{
"command": [
"/cloud_sql_proxy",
"-instances=...",
"-credential_file=..."
],
"image": "gcr.io/cloudsql-docker/gce-proxy:1.11",
"name": "...",
"ports": [
{
"containerPort": 3306,
"protocol": "TCP"
}
],
"volumeMounts": [
{
"mountPath": "/secrets/cloudsql",
"name": "[secrets-mount-name]",
"readOnly": true
}
]
}
],
"volumes": [
{
"name": "[secrets-mount-name]",
"secret": {
"defaultMode": 420,
"secretName": "[secrets-mount-name]"
}
}
]
}
}
}

Answer 1

The error message indicates that your client is not able to trust the certificate of https://www.googleapis.com. There are two possible causes for this:
Your client does not know what root certificates to trust. The official cloudsql-proxy docker image includes root certificates, so if you are using that image, this is not your problem. If you are not using that image, you should (or at least install ca certificates in your image).
Your outbound traffic is being intercepted by a proxy server that is using a different, untrusted, certificate. This might be malicious (in which case you need to investigate who is intercepting your traffic). More benignly, you might be in a organization using an outbound proxy to inspect traffic according to policy. If this is the case, you should build a new docker image that includes the CA certificate used by your organization's outbound proxy.