os-client-config file is not checked on start

[samuelallan72]

When starting the exporter with a path to a non-existant os-client-config file, it happily starts:

ubuntu@juju-92e10b-teststack-18:~$ golang-openstack-exporter.openstack-exporter --os-client-config /this/does/not/exist openstack
ts=2024-03-20T03:23:39.729Z caller=main.go:64 level=info msg="Build context" build_context="(go=go1.22.1, platform=linux/amd64, user=, date=, tags=unknown)"
ts=2024-03-20T03:23:39.729Z caller=main.go:85 level=info msg="openstack exporter started in legacy mode"
ts=2024-03-20T03:23:39.731Z caller=tls_config.go:274 level=info msg="Listening on" address=[::]:9180
ts=2024-03-20T03:23:39.731Z caller=tls_config.go:277 level=info msg="TLS is disabled." http2=false address=[::]:9180

And it only crashes later when the first metrics request comes through:

ubuntu@juju-92e10b-teststack-18:~$ curl http:https://localhost:9180/metrics
curl: (52) Empty reply from server

And the resulting logs:

ts=2024-03-20T03:23:41.753Z caller=main.go:169 level=info msg="Starting openstack exporter version for cloud" version="(version=, branch=, revision=2947f547f4fff606b8d682f2f9e2f6be271b0d83-modified)" cloud=openstack
ts=2024-03-20T03:23:41.754Z caller=main.go:170 level=info msg="Build context" build_context="(go=go1.22.1, platform=linux/amd64, user=, date=, tags=unknown)"
ts=2024-03-20T03:23:41.755Z caller=main.go:184 level=error err="enabling exporter for service failed" service=volume error="unable to load clouds.yaml: open /etc/openstack/clouds.yaml: permission denied"
ts=2024-03-20T03:23:41.755Z caller=main.go:184 level=error err="enabling exporter for service failed" service=container-infra error="unable to load clouds.yaml: open /etc/openstack/clouds.yaml: permission denied"
ts=2024-03-20T03:23:41.756Z caller=main.go:184 level=error err="enabling exporter for service failed" service=baremetal error="unable to load clouds.yaml: open /etc/openstack/clouds.yaml: permission denied"
ts=2024-03-20T03:23:41.756Z caller=main.go:184 level=error err="enabling exporter for service failed" service=orchestration error="unable to load clouds.yaml: open /etc/openstack/clouds.yaml: permission denied"
ts=2024-03-20T03:23:41.757Z caller=main.go:184 level=error err="enabling exporter for service failed" service=image error="unable to load clouds.yaml: open /etc/openstack/clouds.yaml: permission denied"
ts=2024-03-20T03:23:41.758Z caller=main.go:184 level=error err="enabling exporter for service failed" service=load-balancer error="unable to load clouds.yaml: open /etc/openstack/clouds.yaml: permission denied"
ts=2024-03-20T03:23:41.758Z caller=main.go:184 level=error err="enabling exporter for service failed" service=gnocchi error="unable to load clouds.yaml: open /etc/openstack/clouds.yaml: permission denied"
ts=2024-03-20T03:23:41.759Z caller=main.go:184 level=error err="enabling exporter for service failed" service=placement error="unable to load clouds.yaml: open /etc/openstack/clouds.yaml: permission denied"
ts=2024-03-20T03:23:41.759Z caller=main.go:184 level=error err="enabling exporter for service failed" service=object-store error="unable to load clouds.yaml: open /etc/openstack/clouds.yaml: permission denied"
ts=2024-03-20T03:23:41.759Z caller=main.go:184 level=error err="enabling exporter for service failed" service=compute error="unable to load clouds.yaml: open /etc/openstack/clouds.yaml: permission denied"
ts=2024-03-20T03:23:41.760Z caller=main.go:184 level=error err="enabling exporter for service failed" service=identity error="unable to load clouds.yaml: open /etc/openstack/clouds.yaml: permission denied"
ts=2024-03-20T03:23:41.760Z caller=main.go:184 level=error err="enabling exporter for service failed" service=dns error="unable to load clouds.yaml: open /etc/openstack/clouds.yaml: permission denied"
ts=2024-03-20T03:23:41.761Z caller=main.go:184 level=error err="enabling exporter for service failed" service=database error="unable to load clouds.yaml: open /etc/openstack/clouds.yaml: permission denied"
ts=2024-03-20T03:23:41.762Z caller=main.go:184 level=error err="enabling exporter for service failed" service=network error="unable to load clouds.yaml: open /etc/openstack/clouds.yaml: permission denied"
ts=2024-03-20T03:23:41.762Z caller=main.go:194 level=error err="No exporter has been enabled, exiting"

There appear to be a couple of issues here:

• it's still trying to load the default path (/etc/openstack/clouds.yaml) even though a different path has been provided in the flags
• an inaccessible os-client-config file causes an error late (ideally it should crash on startup on this)