Sidecar

 14 minute read

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. In addition, it is possible to restrict the set of services that the proxy can reach when forwarding outbound traffic from workload instances.

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.

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

apiVersion: networking.istio.io/v1alpha3
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 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 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 without any authentication, and HTTPS traffic on port 9443 with one-way TLS termination using custom certificates. To accomplish custom TLS termination on this workload, the PeerAuthentication security policy must be declared to disable Istio mutual TLS on these two ports. Any other auto-generated listener for this workload will still obey the mutual TLS termination requirements set forth in the PeerAuthentication policy. 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/v1alpha3
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
  - port:
      number: 9443
      protocol: HTTPS
      name: httpsport
    inboundTls:
      mode: SIMPLE # overrides namespace default
      serverCertificate: /etc/certs/servercert.pem
      privateKey: /etc/certs/privatekey.pem
    defaultEndpoint: unix:///var/run/someuds.sock
  egress:
  - port:
      number: 9080
      protocol: HTTP
      name: egresshttp
    hosts:
    - "prod-us1/*"
  - hosts:
    - "istio-system/*"

and the associated PeerAuthentication security policy to ensure that mutual TLS based authentication is not configured for ports 9080 and 9443:

apiVersion: security.istio.io/v1beta1
kind: PeerAuthentication
metadata:
  name: ratings-istio-mtls-exception
  namespace: prod-us1
spec:
  selector:
    matchLabels:
      app: ratings
  # other ports inherit the settings from namespace-wide policy.
  portLevelMtls:
    9080:
      mode: DISABLE
    9443:
      mode: DISABLE

and the associated DestinationRule to ensure that the clients use the appropriate TLS settings:

apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: ratings-istio-mtls-exception
  namespace: prod-us1
spec:
  host: ratings.prod-us1.svc.cluster.local
  trafficPolicy:
   portLevelSettings:
   - port:
       number: 9080
     tls:
       mode: DISABLE
   - port:
       number: 9443
     tls:
       mode: SIMPLE
       caCertificates: /etc/certs/ca-certs.pem

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/v1alpha3
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/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: 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

CaptureMode describes how traffic to a listener is expected to be captured. Applicable only when the listener is bound to an IP.

NameDescription
DEFAULT

The default capture mode defined by the environment.

IPTABLES

Capture traffic using IPtables redirection.

NONE

No traffic capture. When used in an egress listener, the application is expected to explicitly communicate with the listener port or Unix domain socket. When used in an ingress listener, care needs to be taken to ensure that the listener port is not in use by other processes on the host.

IstioEgressListener

IstioEgressListener specifies the properties of an outbound traffic listener on the sidecar proxy attached to a workload instance.

FieldTypeDescriptionRequired
portPort

The port associated with the listener. If using Unix domain socket, use 0 as the port number, with a valid protocol. The port if specified, will be used as the default destination port associated with the imported hosts. If the port is omitted, Istio will infer the listener ports based on the imported hosts. Note that when multiple egress listeners are specified, where one or more listeners have specific ports while others have no port, the hosts exposed on a listener port will be based on the listener with the most specific port.

No
bindstring

The IP or the Unix domain socket to which the listener should be bound to. Port MUST be specified if bind is not empty. Format: x.x.x.x or unix:///path/to/uds or unix://@foobar (Linux abstract namespace). If omitted, Istio will automatically configure the defaults based on imported services, the workload instances to which this configuration is applied to and the captureMode. If captureMode is NONE, bind will default to 127.0.0.1.

No
captureModeCaptureMode

When the bind address is an IP, the captureMode option dictates how traffic to the listener is expected to be captured (or not). captureMode must be DEFAULT or NONE for Unix domain socket binds.

No
hostsstring[]

One or more service hosts exposed by the listener in namespace/dnsName format. Services in the specified namespace matching dnsName will be exposed. The corresponding service can be a service in the service registry (e.g., a Kubernetes or cloud foundry service) or a service specified using a ServiceEntry or VirtualService configuration. Any associated DestinationRule in the same namespace will also be used.

The dnsName should be specified using FQDN format, optionally including a wildcard character in the left-most component (e.g., prod/*.example.com). Set the dnsName to * to select all services from the specified namespace (e.g., prod/*).

The namespace can be set to *, ., or ~, representing any, the current, or no namespace, respectively. For example, */foo.example.com selects the service from any available namespace while ./foo.example.com only selects the service from the namespace of the sidecar. If a host is set to */*, Istio will configure the sidecar to be able to reach every service in the mesh that is exported to the sidecar’s namespace. The value ~/* can be used to completely trim the configuration for sidecars that simply receive traffic and respond, but make no outbound connections of their own.

NOTE: Only services and configuration artifacts exported to the sidecar’s namespace (e.g., exportTo value of *) can be referenced. Private configurations (e.g., exportTo set to .) will not be available. Refer to the exportTo setting in VirtualService, DestinationRule, and ServiceEntry configurations for details.

WARNING: The list of egress hosts in a Sidecar must also include the Mixer control plane services if they are enabled. Envoy will not be able to reach them otherwise. For example, add host istio-system/istio-telemetry.istio-system.svc.cluster.local if telemetry is enabled, istio-system/istio-policy.istio-system.svc.cluster.local if policy is enabled, or add istio-system/* to allow all services in the istio-system namespace. This requirement is temporary and will be removed in a future Istio release.

Yes

IstioIngressListener

IstioIngressListener specifies the properties of an inbound traffic listener on the sidecar proxy attached to a workload instance.

FieldTypeDescriptionRequired
portPort

The port associated with the listener.

Yes
bindstring

The IP to which the listener should be bound. Must be in the format x.x.x.x. Unix domain socket addresses are not allowed in the bind field for ingress listeners. If omitted, Istio will automatically configure the defaults based on imported services and the workload instances to which this configuration is applied to.

No
captureModeCaptureMode

The captureMode option dictates how traffic to the listener is expected to be captured (or not).

No
defaultEndpointstring

The loopback IP endpoint or Unix domain socket to which traffic should be forwarded to. This configuration can be used to redirect traffic arriving at the bind IP:Port on the sidecar to a localhost:port or Unix domain socket where the application workload instance is listening for connections. Format should be 127.0.0.1:PORT or unix:///path/to/socket

Yes
inboundTlsTLSOptions

Overrides Sidecar level inboundTls settings. Has same restrictions as the Sidecar level inboundTls, i.e. PeerAuthentication policy takes precedance unless explicitly disabled.

No

OutboundTrafficPolicy

OutboundTrafficPolicy sets the default behavior of the sidecar for handling outbound traffic from the application. If your application uses one or more external services that are not known apriori, setting the policy to ALLOW_ANY will cause the sidecars to route any unknown traffic originating from the application to its requested destination. Users are strongly encouraged to use ServiceEntry configurations to explicitly declare any external dependencies, instead of using ALLOW_ANY, so that traffic to these services can be monitored.

FieldTypeDescriptionRequired
modeModeNo

OutboundTrafficPolicy.Mode

NameDescription
REGISTRY_ONLY

Outbound traffic will be restricted to services defined in the service registry as well as those defined through ServiceEntry configurations.

ALLOW_ANY

Outbound traffic to unknown destinations will be allowed, in case there are no services or ServiceEntry configurations for the destination port.

Sidecar

Sidecar describes the configuration of the sidecar proxy that mediates inbound and outbound communication of the workload instance to which it is attached.

FieldTypeDescriptionRequired
workloadSelectorWorkloadSelector

Criteria used to select the specific set of pods/VMs on which this Sidecar configuration should be applied. If omitted, the Sidecar configuration will be applied to all workload instances in the same namespace.

No
ingressIstioIngressListener[]

Ingress specifies the configuration of the sidecar for processing inbound traffic to the attached workload instance. If omitted, Istio will automatically configure the sidecar based on the information about the workload obtained from the orchestration platform (e.g., exposed ports, services, etc.). If specified, inbound ports are configured if and only if the workload instance is associated with a service.

No
egressIstioEgressListener[]

Egress specifies the configuration of the sidecar for processing outbound traffic from the attached workload instance to other services in the mesh. If not specified, inherits the system detected defaults from the namespace-wide or the global default Sidecar.

No
outboundTrafficPolicyOutboundTrafficPolicy

Configuration for the outbound traffic policy. If your application uses one or more external services that are not known apriori, setting the policy to ALLOW_ANY will cause the sidecars to route any unknown traffic originating from the application to its requested destination. If not specified, inherits the system detected defaults from the namespace-wide or the global default Sidecar.

No
inboundTlsTLSOptions

Set of TLS related options that allow a listener to terminate SIMPLE or MUTUAL TLS connections at the sidecar. PeerAuthentication policy’s settings take precedance over custom TLS settings for the workload. When the PeerAuthentication policy disables mTLS tunneling for one or more ports in the workload, the TLS settings specified here will be applied.

No

WorkloadSelector

WorkloadSelector specifies the criteria used to determine if the Gateway, Sidecar, or EnvoyFilter configuration can be applied to a proxy. The matching criteria includes the metadata associated with a proxy, workload instance info such as labels attached to the pod/VM, or any other info that the proxy provides to Istio during the initial handshake. If multiple conditions are specified, all conditions need to match in order for the workload instance to be selected. Currently, only label based selection mechanism is supported.

FieldTypeDescriptionRequired
labelsmap<string, string>

One or more labels that indicate a specific set of pods/VMs on which this Sidecar configuration should be applied. The scope of label search is restricted to the configuration namespace in which the the resource is present.

Yes
Was this information useful?
Do you have any suggestions for improvement?

Thanks for your feedback!