Add support to setup pod network using VLANs #1125

SaranBalaji90 · 2020-08-07T18:16:45Z

Description of changes:

Issue:
aws/containers-roadmap#177, #208, aws/containers-roadmap#398

Changes included in this PR are as follows,

Creates vlan for pod requesting unique security group.
Skips SNAT for pkts flowing out of Vlan tags, this is to prevent outbound connections from bypassing the egress check.
Supports NodePort for pod backed using Vlan dev.
Adds packet verifier binary to validate the packet flow as part of integration tests.

High level design diagram

Follow-up PRs

Add ipamd changes for sg support #1126

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

* Create vlan for pod requesting unique security group. * Adding packet verifier binary to validate the packet flow as part of integration tests.

mogren

LGTM

cmd/routed-eni-cni-plugin/driver/driver.go

mogren · 2020-08-07T21:18:07Z

cmd/routed-eni-cni-plugin/driver/driver.go

+		return errors.Wrapf(err, "SetupPodENINetwork failed to setup veth pair.")
+	}
+
+	vlanTableId := vlanId + 100


Table names are currently based on Device Index for attached interfaces. Since the maximum number of ENIs for an instance is currently 50, this should be safe.

mogren · 2020-08-07T21:20:17Z

pkg/networkutils/network.go

+	// Prepare the Desired Rule for SNAT Rule for non-pod ENIs
+	snatRule := []string{"!", "-o", "vlan+",
+		"-m", "comment", "--comment", "AWS, SNAT",


This is important, we can't SNAT traffic from pods with Branch ENIs.

Right, what does this affect? Does this mean we can't send traffic outside the immediate VPC from these pods? (that seems bad)

Aside: my quick search just turned up https://docs.aws.amazon.com/eks/latest/userguide/external-snat.html which says:

SNAT is necessary because the internet gateway only knows how to translate between the primary private and public or elastic IP address assigned to the primary elastic network interface of the Amazon EC2 instance node that pods are running on.

Huh, I wouldn't have guessed this limitation, and I couldn't find more info in the VPC docs after a brief search. Is this an IGW limitation, or some side effect of routes that we configure for secondary addresses within CNI? (as in: how will this affect vlan interfaces, if they are configured with the vpc subnet gateway?)

Ingress and Egress permission on the security group is applied to the traffic outside the instance, which means that we can't do any NAT within the instance for these pods. This will bypass the security group check.

If these pods uses private subnet which has NAT gateway associated then traffic will flow out to the internet. Otherwise it can talk only to resources within the VPC.

Thanks, that makes sense. Does that mean we could do the same (NAT at ngw) for secondary IPs, and remove the iptables snat?

Yes we can remove if worker nodes subnets have NAT attached, then we don't have to do this SNAT at the host.

If they have a NAT Gateway, they can set the wonderfully named AWS_VPC_K8S_CNI_EXTERNALSNAT=true, and then aws-node won't set up any SNAT rules (Through this tricky code...).

anguslees

lgtm, nice code.

Some minor comments, but nothing serious.

anguslees · 2020-08-10T10:06:34Z

Makefile

@@ -240,7 +240,7 @@ lint:

 # Run go vet on source code.
 vet:
-	go vet ./...
+	go vet $(ALLPKGS)


why shouldn't packet-verifier pass go vet?

I was seeing the following errors in pcap.go, so going to follow up separately on this with upstream.

# github.com/google/gopacket/pcap ../../../../pkg/mod/github.com/google/[email protected]/pcap/pcap.go:30:22: undefined: pcapErrorNotActivated ../../../../pkg/mod/github.com/google/[email protected]/pcap/pcap.go:52:17: undefined: pcapTPtr ../../../../pkg/mod/github.com/google/[email protected]/pcap/pcap.go:64:10: undefined: pcapPkthdr ../../../../pkg/mod/github.com/google/[email protected]/pcap/pcap.go:102:7: undefined: pcapBpfProgram ../../../../pkg/mod/github.com/google/[email protected]/pcap/pcap.go:103:7: undefined: pcapPkthdr ../../../../pkg/mod/github.com/google/[email protected]/pcap/pcap.go:261:33: undefined: pcapErrorActivated ../../../../pkg/mod/github.com/google/[email protected]/pcap/pcap.go:262:33: undefined: pcapWarningPromisc ../../../../pkg/mod/github.com/google/[email protected]/pcap/pcap.go:263:33: undefined: pcapErrorNoSuchDevice ../../../../pkg/mod/github.com/google/[email protected]/pcap/pcap.go:264:33: undefined: pcapErrorDenied ../../../../pkg/mod/github.com/google/[email protected]/pcap/pcap.go:265:33: undefined: pcapErrorNotUp

cmd/routed-eni-cni-plugin/cni_test.go

cmd/routed-eni-cni-plugin/driver/driver.go

anguslees · 2020-08-10T10:54:31Z

cmd/routed-eni-cni-plugin/driver/driver.go

+
+	// 1. clean up if vlan already exists (necessary when trunk ENI changes).
+	if oldVlan, err := os.netLink.LinkByName(vlanLink.Name); err == nil {
+		if err = os.netLink.LinkDel(oldVlan); err != nil {


Should we ignore 'not found' error here? Or will we end up retrying anyway in that (rare!) case?

If err != nil it will proceed further. Do you mean to say proceed only if err != nil and isNotFound? I can add but thinking it might not be necessary.

cmd/routed-eni-cni-plugin/driver/driver.go

cmd/routed-eni-cni-plugin/driver/driver_test.go

test/cmd/packet-verifier/example/packetverifier_pod.yaml

test/cmd/packet-verifier/packet-verifier.go

anguslees · 2020-08-10T13:12:12Z

test/cmd/packet-verifier/Dockerfile

+RUN go build -o packet-verifier packet-verifier.go
+
+FROM amazonlinux:2
+RUN yum install -y libpcap-devel


Do we need all of libpcap-devel here, or will just the runtime libraries in libpcap do?

I initially tried with just libpcap but that didn't help. Had to pull in couple of dependency from libpcap-devel as well.

SaranBalaji90 · 2020-08-10T17:02:49Z

lgtm, nice code.

Some minor comments, but nothing serious.

Thank you :)

mogren · 2020-08-10T17:30:06Z

cmd/routed-eni-cni-plugin/driver/driver.go

+	// 2. delete two ip rules associated with the vlan
+	vlanRule := os.netLink.NewRule()
+	vlanRule.Table = vlanId + 100
+	vlanRule.Priority = vlanRulePriority
+
+	for {
+		if err := os.netLink.RuleDel(vlanRule); err != nil {
+			if !containsNoSuchRule(err) {
+				return errors.Wrapf(err, "TeardownPodENINetwork: failed to delete container rule for %d", vlanId)
+			}
+			break
+		}
+	}


This is slightly tricky and it would be nice to have a comment explaining how it works. Basically, we create a new route table for each vlan in SetupPodENINetwork(). The table only has two rules, defined in buildRoutesForVlan(). When we tear down, we want to delete both those rules. Calling netLink.RuleDel with only the table name and priority will delete the first rule matching that, that's why we have the for-loop.

* Changes include: * Create vlan for pod requesting unique security group. * Adding packet verifier binary to validate the packet flow as part of integration tests.

SaranBalaji90 requested review from anguslees, jaypipes and mogren August 7, 2020 18:17

SaranBalaji90 changed the title ~~Add support to setup pod network based on Vlan ID~~ Add support to setup pod network using VLANs Aug 7, 2020

SaranBalaji90 force-pushed the vlan-cni branch 2 times, most recently from 5ef3b1f to 4dd10e8 Compare August 7, 2020 19:46

Changes include:

2fa7981

* Create vlan for pod requesting unique security group. * Adding packet verifier binary to validate the packet flow as part of integration tests.

SaranBalaji90 force-pushed the vlan-cni branch from 4dd10e8 to 2fa7981 Compare August 7, 2020 20:23

mogren approved these changes Aug 7, 2020

View reviewed changes

mogren mentioned this pull request Aug 8, 2020

Add ipamd changes for sg support #1126

Merged

anguslees reviewed Aug 10, 2020

View reviewed changes

mogren approved these changes Aug 10, 2020

View reviewed changes

Incorporating feedback.

130b4e2

SaranBalaji90 force-pushed the vlan-cni branch from 57f9585 to 130b4e2 Compare August 10, 2020 19:31

mogren merged commit ad4802b into aws:master Aug 10, 2020

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Add support to setup pod network using VLANs #1125

Add support to setup pod network using VLANs #1125

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Add support to setup pod network using VLANs #1125

Add support to setup pod network using VLANs #1125

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