[Policy Assistant] warn about same-priority ANPs with overlapping rules

[huntergregory]

Parent issue: #150

This issue is derived from discussions in #216.

Proposal

Policy Assistant should be able to let admins know if any of their AdminNetworkPolicies have undefined/implementation-specific behavior (exact terminology TBD in #216).

Example

Command like:

policy-assistant analyze --mode=overlap --all-namespaces --all-pods

with output like:

INFO: detected AdminNetworkPolicies with the same priority. checking for overlapping rules
INFO: no overlapping rules found
WARN: analyzed only on the cluster's current set of Pods/labels (relabeling Pods might change this result)

or

INFO: detected AdminNetworkPolicies with the same priority. checking for overlapping rules
WARN: detected implementation-specific behavior for these AdminNetworkPolicies due to overlapping rules. policies: [anp-1 (allow-some-rule), anp-2 (deny-all-rule)]. pods: [kube-system/deployment/core-dns, test-namespace/daemonset/backend]
WARN: detected implementation-specific behavior for these AdminNetworkPolicies ...
...
WARN: analyzed only on the cluster's current set of Pods/labels (relabeling Pods might change this result)

[huntergregory]

Could use help in implementing this. The feature requires the following:

1. First, we must start allowing ANPs with the same priority. Right here, we should instead log that there "may be overlapping rules" and suggest the --mode=overlap command:
   

   network-policy-api/cmd/policy-assistant/pkg/matcher/builder.go

   Line 27 in 669dfbc

   panic(errors.Errorf("duplicate priorities are undefined. priority: %d", p.Spec.Priority))

2. Write a function keeping track of all rules that share the same priority for the given traffic, similar to Resolve():
   

   network-policy-api/cmd/policy-assistant/pkg/matcher/policy.go

   Lines 163 to 187 in 669dfbc

   	func (d DirectionResult) Resolve() (*Effect, *Effect, *Effect) {
   	if d == nil {
   	return nil, nil, nil
   	}
   	// 1. ANP rules
   	var anpEffect *Effect
   	for _, e := range d {
   	if e.PolicyKind != AdminNetworkPolicy {
   	continue
   	}
   	if anpEffect == nil {
   	anpEffect = &Effect{
   	PolicyKind: AdminNetworkPolicy,
   	Verdict: None,
   	Priority: maxInt,
   	}
   	}
   	if e.Verdict != None && e.Priority < anpEffect.Priority {
   	eCopy := e
   	anpEffect = &eCopy
   	}
   	}

3. Create a --mode=overlap option for similar to --mode=explain:
   

   network-policy-api/cmd/policy-assistant/pkg/cli/analyze.go

   Lines 138 to 140 in 669dfbc

   	case ExplainMode:
   	fmt.Println("explained policies:")
   	ExplainPolicies(policies)

We can start with implementing this for a single "traffic". See this struct:

network-policy-api/cmd/policy-assistant/pkg/matcher/traffic.go

Line 13 in 669dfbc

type Traffic struct {

May need to hard-code Traffic and AdminNetworkPolicies for now (some examples at example.go)