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78 lines
2.9 KiB
Go
78 lines
2.9 KiB
Go
//go:build linux
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/*
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Copyright (c) Edgeless Systems GmbH
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SPDX-License-Identifier: AGPL-3.0-only
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*/
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package azure
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import (
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"context"
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"fmt"
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"log/slog"
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"github.com/edgelesssys/constellation/v2/internal/role"
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"k8s.io/kubernetes/pkg/util/iptables"
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"k8s.io/utils/exec"
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)
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// PrepareControlPlaneNode sets up iptables for the control plane node only
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// if an internal load balancer is used.
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//
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// This is needed since during `kubeadm init` the API server must talk to the
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// kubeAPIEndpoint, which is the load balancer IP address. During that time, the
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// only healthy VM is the VM itself. Therefore, traffic is sent to the load balancer
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// and the 5-tuple is (VM IP, <some port>, LB IP, 6443, TCP).
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// Now the load balancer does not re-write the source IP address only the destination (DNAT).
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// Therefore the 5-tuple is (VM IP, <some port>, VM IP, 6443, TCP).
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// Now the VM responds to the SYN packet with a SYN-ACK packet, but the outgoing
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// connection waits on a response from the load balancer and not the VM therefore
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// dropping the packet.
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//
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// OpenShift also uses the same mechanism to redirect traffic to the API server:
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// https://github.com/openshift/machine-config-operator/blob/e453bd20bac0e48afa74e9a27665abaf454d93cd/templates/master/00-master/azure/files/opt-libexec-openshift-azure-routes-sh.yaml
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func (c *Cloud) PrepareControlPlaneNode(ctx context.Context, log *slog.Logger) error {
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selfMetadata, err := c.Self(ctx)
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if err != nil {
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return fmt.Errorf("failed to get self metadata: %w", err)
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}
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// skipping iptables setup for worker nodes
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if selfMetadata.Role != role.ControlPlane {
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log.Info("not a control plane node, skipping iptables setup")
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return nil
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}
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// skipping iptables setup if no internal LB exists e.g.
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// for public LB architectures
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loadbalancerIP, err := c.getLoadBalancerPrivateIP(ctx)
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if err != nil {
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log.With(slog.Any("error", err)).Warn("skipping iptables setup, failed to get load balancer private IP")
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return nil
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}
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log.Info(fmt.Sprintf("Setting up iptables for control plane node with load balancer IP %s", loadbalancerIP))
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iptablesExec := iptables.New(exec.New(), iptables.ProtocolIPv4)
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const chainName = "azure-lb-nat"
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if _, err := iptablesExec.EnsureChain(iptables.TableNAT, chainName); err != nil {
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return fmt.Errorf("failed to create iptables chain: %w", err)
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}
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if _, err := iptablesExec.EnsureRule(iptables.Append, iptables.TableNAT, "PREROUTING", "-j", chainName); err != nil {
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return fmt.Errorf("failed to add rule to iptables chain: %w", err)
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}
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if _, err := iptablesExec.EnsureRule(iptables.Append, iptables.TableNAT, "OUTPUT", "-j", chainName); err != nil {
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return fmt.Errorf("failed to add rule to iptables chain: %w", err)
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}
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if _, err := iptablesExec.EnsureRule(iptables.Append, iptables.TableNAT, chainName, "--dst", loadbalancerIP, "-p", "tcp", "--dport", "6443", "-j", "REDIRECT"); err != nil {
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return fmt.Errorf("failed to add rule to iptables chain: %w", err)
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}
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return nil
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}
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