java.io.IOException: Failed to retrieve API configs with status: 404 when called from webserver - google-app-engine

Question

So I have an appengine webapp which includes cloud endpoints deployed locally on port 8888.
The error message in the title occurs on startup of our webpack-dev-server which runs on port 3000 and proxies all requests starting with /_ah/api/* to http://localhost:8888. The exact console error is as follows:
The odd thing is, when I open this url in another tab and switch the port to 8888 the request comes through, and the webpack-dev-server can also proxy the requests to the backend from then on.
Most other issues I read on this suggested setting the appengine config in gradle to the following:
httpPort = 8888
httpAddress = "0.0.0.0";
However I already did that so that does not seem to be the issue.
My relevant webpack config is as follows:
module.exports = webpackMerge(commonConfig, {
...
output: {
...
publicPath: 'http://localhost:3000/'
},
devServer: {
port: 3000,
open: true,
proxy: {
'/_ah/api/*': 'http://localhost:8888/'
}
}
});

Answer 1

Some backends don't work properly without changeOrigin: true. You can use it like this:
proxy: {
'/_ah/api/*': {
target: 'http://localhost:8888/',
changeOrigin: true,
secure: false
}
}
If that doesn't work, does the proxy path (/_ah/api/) need to be included in the request? You could try if ignoring the path works:
proxy: {
'/_ah/api/*': {
target: 'http://localhost:8888/',
ignorePath: true
}
}
And if that doesn't work, I would try out removing the last part of the proxy path: /_ah/api/* to /_ah/api. This should do the same, but the first one is deprecated.