我尝试了很多事情，但似乎无法通过Exception while connectingGoogle Cloud App Engine连接到Google Cloud PostgreSQL实例。

作为开发人员，这可能是我经历过的最令人沮丧的事情。连接数据库并不难。

我究竟做错了什么？

无效的事情：

• 如何通过Google App Engine Flex将Google Cloud SQL连接到僵尸网络核心应用程序？
• 无法从Google App Engine节点连接到Cloud sql中的Postgres
• https://cloud.google.com/sql/docs/postgres/connect-app-engine-flexible
• https://github.com/GoogleCloudPlatform/dotnet-docs-samples/tree/master/appengine/flexible/CloudSql

app.yaml：

runtime: custom
env: flex
beta_settings:
  cloud_sql_instances: "<project-id>:<region>:<sql-instance>=tcp:5432"

最终使用的连接字符串：

Uid=<db_user>;Pwd=<db_password>;Host=cloudsql;Database=<db_name>

// other attempts:
Uid=<db_user>;Pwd=<db_password>;Host=cloudsql;Database=<db_name>;Port=5432
Uid=<db_user>;Pwd=<db_password>;Host=/cloudsql/<project-id>:<region>:<sql-instance>;Database=<db_name>
Uid=<db_user>;Pwd=<db_password>;Host='/cloudsql/<project-id>:<region>:<sql-instance>';Database=<db_name>
Uid=<db_user>;Pwd=<db_password>;Server='/cloudsql/<project-id>:<region>:<sql-instance>';Database=<db_name>

用法：

var connectionString = new NpgsqlConnectionStringBuilder(<connection string>)
{
    SslMode = SslMode.Disable
};

NpgsqlConnection connection =
    new NpgsqlConnection(connectionString.ConnectionString);

connection.Open();

相关堆栈跟踪：

Exception while connecting
   at Npgsql.NpgsqlConnector.Connect(NpgsqlTimeout timeout)
   at Npgsql.NpgsqlConnector.RawOpen(NpgsqlTimeout timeout, Boolean async, CancellationToken cancellationToken)
   at Npgsql.NpgsqlConnector.Open(NpgsqlTimeout timeout, Boolean async, CancellationToken cancellationToken)
   at Npgsql.ConnectorPool.AllocateLong(NpgsqlConnection conn, NpgsqlTimeout timeout, Boolean async, CancellationToken cancellationToken)
   at Npgsql.NpgsqlConnection.<>c__DisplayClass32_0.<g__OpenLong|0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Npgsql.NpgsqlConnection.Open()

Dockerfile（也许它很重要，因为我用custom我的app.yaml runtime？）：

FROM mcr.microsoft.com/dotnet/core/aspnet:3.1-buster-slim AS base
WORKDIR /app
EXPOSE 80
EXPOSE 8080
EXPOSE 443
ENV ASPNETCORE_URLS=http://*:8080

FROM mcr.microsoft.com/dotnet/core/sdk:3.1-buster AS build
COPY . /src
WORKDIR /src
RUN dotnet restore --packages /packages
RUN dotnet publish -c Release -o /published

FROM base AS final
COPY --from=build /published /app/
WORKDIR /app
ENTRYPOINT [ "dotnet", "myapp.dll" ]

部署脚本：

gcloud beta app deploy --project <project-id>

编辑：

从云控制台检查sql实例的PostgreSQL错误，我在最终Exception while connecting错误之前看到以下错误：

System.Net.Internals.SocketExceptionFactory+ExtendedSocketException (99): Cannot assign requested address /cloudsql/<my connection instance id>/.s.PGSQL.5432