Guarrant a client conn always send request to same backend
+
Minimize remapping
+
+
+### Proposal
+
+#### maglev
+Algorithm main purpose: map all backends into a fixed look up table, require even mapping, and try to minimize mapping changes when backend change (remove or add a backend), avoid global remapping.
+
+
+#### ebpf implement situation or point
+
+
Cgroup level
+In cgroup socket implement l4 and l7 header based consistent hash.
+
Container veth tc level
+In tc level implement l4 based and l7 based consistent hash.
+
+
+
+### Design Details
+
+
+#### maglev
+main steps:
+
+
+
Map endpoints of Cluster to a fixed table
+Based on Cluster config from istiod to generate a integer table, the value of table is endpoints index;
+
+
+
Base l4 or l7 info compute a hash value
+use hash value get an table index, which is index=hash%len(table);
+
Use index to access table
+ep=tables[index]
+
+
+
+##### maglev lookup table
+Use a compact table, table entry is bit width of endpoint count.
+For the table size default is 16381.
+
+#### L4 implement
+
+
(saddr,daddr,sport,dport,protocol)-->hash
+
then execute above second step.
+
+
+##### risk in l4 implement
+In cgroup level, because of lacking saddr and sport, can't do l4 lb effectively.
+
+By the advice of @supercharge-xsy, add (net namespace cookie + daddr + dport ) to compute hash value.
+
+
+#### L7 implement
+```
+apiVersion: networking.istio.io/v1alpha3
+kind: DestinationRule
+metadata:
+ name: helloworld
+spec:
+ host: helloworld
+ trafficPolicy:
+ loadBalancer:
+ consistentHash:
+ httpHeaderName: testHeader
+ maglev:
+ tableSize:
+```
+
+
specify which l7 header is selected to do hash
+
extract l7 header info from http header
+
compute a hash value base header value
+
then execute above second step
+
+
+##### Risk in l7 header value to compute a hash
+Because in ebpf prog, there is a lack of string-based hash compute.
+
+Below is a simple string-based hash method.Probability we need an effective hash method.
+```
+static inline __u32 lb_hash_based_header(unsigned char *header_name) {
+ __u32 hash = 0;
+ struct bpf_mem_ptr *msg_header = NULL;
+ char *msg_header_v = NULL;
+ __u32 msg_header_len = 0;
+ __u32 k;
+ __u32 c;
+ char msg_header_cp[KMESH_PER_HASH_POLICY_MSG_HEADER_LEN] = {'\0'};
+
+ if (!header_name)
+ return hash;
+ // when header name is not null, compute a hash value.
+ BPF_LOG(INFO, ROUTER_CONFIG, "Got a header name:%s\n", header_name);
+ msg_header = (struct bpf_mem_ptr *)bpf_get_msg_header_element(header_name);
+ if (!msg_header)
+ return hash;
+
+ msg_header_v = _(msg_header->ptr);
+ msg_header_len = _(msg_header->size);
+ if (!msg_header_len)
+ return hash;
+
+ BPF_LOG(INFO, ROUTER_CONFIG, "Got a header value len:%u\n", msg_header_len);
+ if (!bpf_strncpy(msg_header_cp, msg_header_len, msg_header_v))
+ return hash;
+ BPF_LOG(INFO, ROUTER_CONFIG, "Got a header value:%s\n", msg_header_cp);
+ // Currently a simple hash method
+ hash = 5318;
+# pragma unroll
+ for (k = 0; k < KMESH_PER_HASH_POLICY_MSG_HEADER_LEN;k++) {
+ if (!msg_header_v || k >= msg_header_len)
+ break;
+ c = *((unsigned char *)msg_header_cp + k);
+ hash = ((hash << 5) + hash) + c;
+ }
+
+ return hash;
+}
+```
+
+
+#### Cgroup level
+Directly through lb logic, to change the daddr and dport of socket.
+
+#### Tc level
+Do lb algorithm based on network packet or message, to change the daddr and dport of packet.
+
+This way can get full ip address info to do lb.
+
+#### Test Plan
+
+
+
Table mapping is even distribution
+
Add or remove a endpoint only affect few connections