Sidecar

Sidecar describes the configuration of the sidecar proxy that mediates inbound and outbound communication to the workload it is attached to. By default, Istio will program all sidecar proxies in the mesh with the necessary configuration required to reach every workload in the mesh, as well as accept traffic on all the ports associated with the workload. The Sidecar resource provides a way to fine tune the set of ports, protocols that the proxy will accept when forwarding traffic to and from the workload. In addition, it is possible to restrict the set of services that the proxy can reach when forwarding outbound traffic from the workload.

Services and configuration in a mesh are organized into one or more namespaces (e.g., a Kubernetes namespace or a CF org/space). A Sidecar resource in a namespace will apply to one or more workloads in the same namespace, selected using the workloadSelector. In the absence of a workloadSelector, it will apply to all workloads in the same namespace. When determining the Sidecar resource to be applied to a workload, preference will be given to the resource with a workloadSelector that selects this workload, over a Sidecar resource without any workloadSelector.

NOTE: Each namespace can have only one Sidecar resource without any workload selector. The behavior of the system is undefined if more than one selector-less Sidecar resources exist in a given namespace. The behavior of the system is undefined if two or more Sidecar resources with a workload selector select the same workload.

The example below declares a Sidecar resource in the prod-us1 namespace that configures the sidecars in the namespace to allow egress traffic to public services in the prod-us1, prod-apis, and the istio-system namespaces.

apiVersion: networking.istio.io/v1alpha3
kind: Sidecar
metadata:
  name: default
  namespace: prod-us1
spec:
  egress:
  - hosts:
    - "prod-us1/*"
    - "prod-apis/*"
    - "istio-system/*"

The example below declares a Sidecar resource in the prod-us1 namespace that accepts inbound HTTP traffic on port 9080 and forwards it to the attached workload listening on a Unix domain socket. In the egress direction, in addition to the istio-system namespace, the sidecar proxies only HTTP traffic bound for port 9080 for services in the prod-us1 namespace.

apiVersion: networking.istio.io/v1alpha3
kind: Sidecar
metadata:
  name: default
  namespace: prod-us1
spec:
  ingress:
  - port:
      number: 9080
      protocol: HTTP
      name: somename
    defaultEndpoint: unix:///var/run/someuds.sock
  egress:
  - hosts:
    - "istio-system/*"
  - port:
      number: 9080
      protocol: HTTP
      name: egresshttp
    hosts:
    - "prod-us1/*"

If the workload is deployed without IP tables based traffic capture, the Sidecar resource is the only way to configure the ports on the proxy attached to the workload. The following example declares a Sidecar resource in the prod-us1 namespace for all pods with labels “app: productpage” belonging to the productpage.prod-us1 service. Assuming that these pods are deployed without IPtable rules (i.e. the Istio init container) and the proxy metadata ISTIO_META_INTERCEPTION_MODE is set to NONE, the specification below allows such pods to receive HTTP traffic on port 9080 and forward it to the application listening on 127.0.0.1:8080. It also allows the application to communicate with a backing MySQL database on 127.0.0.1:3306, that then gets proxied to the externally hosted MySQL service at mysql.foo.com:3306.

apiVersion: networking.istio.io/v1alpha3
kind: Sidecar
metadata:
  name: no-ip-tables
  namespace: prod-us1
spec:
  workloadSelector:
    labels:
      app: productpage
  ingress:
  - port:
      number: 9080 # binds to 0.0.0.0:9080
      protocol: HTTP
      name: somename
    defaultEndpoint: 127.0.0.1:8080
    captureMode: NONE # not needed if metadata is set for entire proxy
  egress:
  - port:
      number: 3306
      protocol: MYSQL
      name: egressmysql
    captureMode: NONE # not needed if metadata is set for entire proxy
    bind: 127.0.0.1
    hosts:
    - "*/mysql.foo.com"

And the associated service entry for routing to mysql.foo.com:3306

apiVersion: networking.istio.io/v1alpha3
kind: ServiceEntry
metadata:
  name: external-svc-mysql
  namespace: ns1
spec:
  hosts:
  - mysql.foo.com
  ports:
  - number: 3306
    name: mysql
    protocol: MYSQL
  location: MESH_EXTERNAL
  resolution: DNS

It is also possible to mix and match traffic capture modes in a single proxy. For example, consider a setup where internal services are on the 192.168.0.0/16 subnet. So, IP tables are setup on the VM to capture all outbound traffic on 192.168.0.0/16 subnet. Assume that the VM has an additional network interface on 172.16.0.0/16 subnet for inbound traffic. The following Sidecar configuration allows the VM to expose a listener on 172.16.1.32:80 (the VM’s IP) for traffic arriving from the 172.16.0.0/16 subnet. Note that in this scenario, the ISTIO_META_INTERCEPTION_MODE metadata on the proxy in the VM should contain “REDIRECT” or “TPROXY” as its value, implying that IP tables based traffic capture is active.

apiVersion: networking.istio.io/v1alpha3
kind: Sidecar
metadata:
  name: partial-ip-tables
  namespace: prod-us1
spec:
  workloadSelector:
    labels:
      app: productpage
  ingress:
  - bind: 172.16.1.32
    port:
      number: 80 # binds to 172.16.1.32:80
      protocol: HTTP
      name: somename
    defaultEndpoint: 127.0.0.1:8080
    captureMode: NONE
  egress:
    # use the system detected defaults
    # sets up configuration to handle outbound traffic to services
    # in 192.168.0.0/16 subnet, based on information provided by the
    # service registry
  - captureMode: IPTABLES
    hosts:
    - "*/*"

CaptureMode

IstioEgressListener

IstioIngressListener

Sidecar

WorkloadSelector