func tryPopulateUnspecifiedFromMetadata()

in pkg/export/setup/setup.go [333:396]
45 lines of code
10 McCabe index (conditional complexity)

func tryPopulateUnspecifiedFromMetadata(ctx context.Context, logger log.Logger, opts *export.ExporterOpts) {
	const (
		projectIDPath       = "project/project-id"
		clusterNamePath     = "instance/attributes/cluster-name"
		clusterLocationPath = "instance/attributes/cluster-location"
		zonePath            = "instance/zone"
	)

	env := UAEnvGCE // This also means GKE with metadata server disabled.

	c := metadata.NewClient(nil)
	// Mimick metadata.InstanceAttributeValue("cluster-name") but with context.
	gkeClusterName, err := c.GetWithContext(ctx, clusterNamePath)
	if err != nil {
		_ = level.Debug(logger).Log("msg", "fetching entry from GCP metadata server failed; skipping", "key", clusterNamePath, "err", err)
	} else if gkeClusterName != "" {
		env = UAEnvGKE
		if opts.Cluster == "" {
			opts.Cluster = gkeClusterName
		}
	}

	if opts.ProjectID == "" {
		// Mimick metadata.ProjectID() but with context.
		projectID, err := c.GetWithContext(ctx, projectIDPath)
		if err != nil {
			_ = level.Debug(logger).Log("msg", "fetching entry from GCP metadata server failed; skipping", "key", projectIDPath, "err", err)
		} else {
			opts.ProjectID = strings.TrimSpace(projectID)
		}
	}
	if opts.Location == "" {
		// These attributes are set for GKE nodes. For the location, we first check
		// the cluster location, which may be a zone or a region. We must always use that value
		// to avoid collisions with other clusters, as the same cluster name may be reused
		// in different locations.
		// In particular, we cannot set the location to the node's zone for a regional cluster,
		// even though this would provide more accuracy, as there may also be a zonal cluster
		// with the same name.
		//
		// We only fallback to the node zone as the location if no cluster location exists to
		// default for deployments on GCE.

		// Mimick metadata.InstanceAttributeValue("cluster-location") but with context.
		loc, err := c.GetWithContext(ctx, clusterLocationPath)
		if err != nil {
			_ = level.Debug(logger).Log("msg", "fetching entry from GCP metadata server failed; falling back to zone", "key", clusterLocationPath, "err", err)
			zone, err := c.GetWithContext(ctx, zonePath)
			if err != nil {
				_ = level.Debug(logger).Log("msg", "fetching entry from GCP metadata server failed; skipping", "key", zonePath, "err", err)
			} else {
				zone = strings.TrimSpace(zone)
				// zone is of the form "projects/<projNum>/zones/<zoneName>".
				opts.Location = zone[strings.LastIndex(zone, "/")+1:]
			}
		} else {
			opts.Location = loc
		}
	}
	if opts.UserAgentEnv == UAEnvUnspecified {
		// We acknowledge that, if user set unspecified on purpose, this will override.
		opts.UserAgentEnv = env
	}
}