Sidecar

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

One the common usages of Sidecar is to limit the set of configuration for outbound traffic. This configuration scoping, among other options, is useful to prune out unneeded configuration, to improve scalability of the mesh. A common misunderstanding is that restricting the configuration amounts to blocking the traffic. If requests are sent to destinations not included in the scoping, the traffic will be treated as unmatched traffic, which is often still allowed. The sidecar is not able to enforce an outbound traffic restriction (see Egress Gateways for how to achieve this).

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 configuration in a namespace will apply to one or more workload instances in the same namespace, selected using the workloadSelector field. In the absence of a workloadSelector, it will apply to all workload instances in the same namespace. When determining the Sidecar configuration to be applied to a workload instance, preference will be given to the resource with a workloadSelector that selects this workload instance, over a Sidecar configuration without any workloadSelector.

NOTE 1: Each namespace can have only one Sidecar configuration without any workloadSelector that specifies the default for all pods in that namespace. It is recommended to use the name default for the namespace-wide sidecar. The behavior of the system is undefined if more than one selector-less Sidecar configurations exist in a given namespace. The behavior of the system is undefined if two or more Sidecar configurations with a workloadSelector select the same workload instance.

NOTE 2: A Sidecar configuration in the MeshConfig root namespace will be applied by default to all namespaces without a Sidecar configuration. This global default Sidecar configuration should not have any workloadSelector.

NOTE 3: A Sidecar is not applicable to gateways, even though gateways are istio-proxies.

The example below declares a global default Sidecar configuration in the root namespace called istio-config, that configures sidecars in all namespaces to configure egress traffic only to other workloads in the same namespace as well as to services in the istio-system namespace.

apiVersion: networking.istio.io/v1
kind: Sidecar
metadata:
  name: default
  namespace: istio-config
spec:
  egress:
  - hosts:
    - "./*"
    - "istio-system/*"

The example below declares a Sidecar configuration in the prod-us1 namespace that overrides the global default defined above, and configures the sidecars in the namespace to configure egress traffic to public services in the prod-us1, prod-apis, and the istio-system namespaces.

apiVersion: networking.istio.io/v1
kind: Sidecar
metadata:
  name: default
  namespace: prod-us1
spec:
  egress:
  - hosts:
    - "prod-us1/*"
    - "prod-apis/*"
    - "istio-system/*"

The following example declares a Sidecar configuration in the prod-us1 namespace for all pods with labels app: ratings belonging to the ratings.prod-us1 service. The workload accepts inbound HTTP traffic on port 9080. The traffic is then forwarded to the attached workload instance 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/v1
kind: Sidecar
metadata:
  name: ratings
  namespace: prod-us1
spec:
  workloadSelector:
    labels:
      app: ratings
  ingress:
  - port:
      number: 9080
      protocol: HTTP
      name: somename
    defaultEndpoint: unix:///var/run/someuds.sock
  egress:
  - port:
      number: 9080
      protocol: HTTP
      name: egresshttp
    hosts:
    - "prod-us1/*"
  - hosts:
    - "istio-system/*"

If the workload is deployed without IPTables-based traffic capture, the Sidecar configuration is the only way to configure the ports on the proxy attached to the workload instance. The following example declares a Sidecar configuration 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 (wrapped inside Istio mutual TLS) 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/v1
kind: Sidecar
metadata:
  name: no-ip-tables
  namespace: prod-us1
spec:
  workloadSelector:
    labels:
      app: productpage
  ingress:
  - port:
      number: 9080 # binds to proxy_instance_ip:9080 (0.0.0.0:9080, if no unicast IP is available for the instance)
      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/v1
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: 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/v1
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:
    - "*/*"

The following example declares a Sidecar configuration in the prod-us1 namespace for all pods with labels app: ratings belonging to the ratings.prod-us1 service. The service accepts inbound HTTPS traffic on port 8443 and the sidecar proxy terminates one way TLS using the given server certificates. The traffic is then forwarded to the attached workload instance listening on a Unix domain socket. It is expected that PeerAuthentication policy would be configured in order to set mTLS mode to “DISABLE” on specific ports. In this example, the mTLS mode is disabled on PORT 80. This feature is currently experimental.

apiVersion: networking.istio.io/v1
kind: Sidecar
metadata:
  name: ratings
  namespace: prod-us1
spec:
  workloadSelector:
    labels:
      app: ratings
  ingress:
  - port:
      number: 80
      protocol: HTTPS
      name: somename
    defaultEndpoint: unix:///var/run/someuds.sock
    tls:
      mode: SIMPLE
      privateKey: "/etc/certs/privatekey.pem"
      serverCertificate: "/etc/certs/servercert.pem"
---
apiVersion: v1
kind: Service
metadata:
  name: ratings
  labels:
    app: ratings
    service: ratings
spec:
  ports:
  - port: 8443
    name: https
    targetPort: 80
  selector:
    app: ratings
---
apiVersion: security.istio.io/v1
kind: PeerAuthentication
metadata:
  name: ratings-peer-auth
  namespace: prod-us1
spec:
  selector:
    matchLabels:
      app: ratings
  mtls:
    mode: STRICT
  portLevelMtls:
    80:
      mode: DISABLE

In addition to configuring traffic capture and how traffic is forwarded to the app, it’s possible to control inbound connection pool settings. By default, Istio pushes connection pool settings from DestinationRules to both clients (for outbound connections to the service) as well as servers (for inbound connections to a service instance). Using the InboundConnectionPool and per-port ConnectionPool settings in a Sidecar allow you to control those connection pools for the server separately from the settings pushed to all clients.

apiVersion: networking.istio.io/v1
kind: Sidecar
metadata:
  name: connection-pool-settings
  namespace: prod-us1
spec:
  workloadSelector:
    labels:
      app: productpage
  inboundConnectionPool:
      http:
        http1MaxPendingRequests: 1024
        http2MaxRequests: 1024
        maxRequestsPerConnection: 1024
        maxRetries: 100
  ingress:
  - port:
      number: 80
      protocol: HTTP
      name: somename
    connectionPool:
      http:
        http1MaxPendingRequests: 1024
        http2MaxRequests: 1024
        maxRequestsPerConnection: 1024
        maxRetries: 100
      tcp:
        maxConnections: 100

Sidecar

IstioIngressListener

IstioEgressListener

WorkloadSelector

OutboundTrafficPolicy

Mode

SidecarPort

CaptureMode