Yggdrasil is an Envoy control plane that configures listeners and clusters based off Kubernetes ingresses from multiple Kube Clusters. This allows you to have an envoy cluster acting as a mutli-cluster loadbalancer for Kubernetes. This was something we needed as we wanted our apps to be highly available in the event of a cluster outage but did not want the solution to live inside of Kubernetes itself.
Note: Currently we support versions 1.20.x to 1.26.x of Envoy.
Note: Yggdrasil now uses Go modules to handle dependencies.
Yggdrasil will watch all Ingresses in each Kubernetes Cluster that you give it via the Kubeconfig flag. Any ingresses that match any of the ingress classes that you have specified will have a listener and cluster created that listens on the same Host as the Host defined in the Ingress object. If you have multiple clusters Yggdrasil will create a cluster address for each Kubernetes cluster your Ingress is in, the address is the address of the ingress loadbalancer.
Joseph Irving has published a blog post which describes our need for and use of Yggdrasil at Uswitch.
Please see the Getting Started guide for a walkthrough of setting up a simple HTTP service with Yggdrasil and envoy.
The basic setup is to have a cluster of envoy nodes which connect to Yggdrasil via GRPC and get given dynamic listeners and clusters from it. Yggdrasil is set up to talk to each Kubernetes api where it will watch the ingresses for any that are using the ingress class it's watching for.
Your envoy nodes only need a very minimal config where they are simply set up to get dynamic clusters and listeners from Yggdrasil. Example envoy config:
admin:
access_log_path: /tmp/admin_access.log
address:
socket_address: { address: 0.0.0.0, port_value: 9901 }
dynamic_resources:
lds_config:
resource_api_version: V3
api_config_source:
transport_api_version: V3
api_type: GRPC
grpc_services:
- envoy_grpc:
cluster_name: xds_cluster
cds_config:
resource_api_version: V3
api_config_source:
transport_api_version: V3
api_type: GRPC
grpc_services:
- envoy_grpc:
cluster_name: xds_cluster
static_resources:
clusters:
- name: xds_cluster
connect_timeout: 0.25s
type: STATIC
lb_policy: ROUND_ROBIN
http2_protocol_options: {}
load_assignment:
cluster_name: xds_cluster
endpoints:
- lb_endpoints:
- endpoint:
address:
socket_address:
address: yggdrasil
port_value: 8080Your ingress set up then looks like this:
Where the envoy nodes are loadbalancing between each cluster for a given ingress.
Yggdrasil always configures a path on your Envoy nodes at /yggdrasil/status, this can be used to health check your envoy nodes, it will only return 200 if your nodes have started and been configured by Yggdrasil.
Yggdrasil allows for some customisation of the route and cluster config per Ingress through the annotations below.
| Name | type |
|---|---|
| yggdrasil.uswitch.com/healthcheck-path | string |
| yggdrasil.uswitch.com/timeout | duration |
| yggdrasil.uswitch.com/retry-on | string |
Specifies a path to configure a HTTP health check to. Envoy will not route to clusters that fail health checks.
Allows for adjusting the timeout in envoy. Currently this will set the following timeouts to this value:
- config.route.v3.RouteAction.Timeout
- config.route.v3.RetryPolicy.PerTryTimeout
- config.cluster.v3.Cluster.ConnectTimeout
Allows overwriting the default retry policy's config.route.v3.RetryPolicy.RetryOn set by the --retry-on flag (default 5xx). Accepts a comma-separated list of retry-on policies.
Below is an example of an ingress with some of the annotations specified
apiVersion: extensions/v1beta1
kind: Ingress
metadata:
name: example-com
namespace: default
annotations:
yggdrasil.uswitch.com/healthcheck-path: /healthz
yggdrasil.uswitch.com/timeout: 30s
yggdrasil.uswitch.com/retry-on: gateway-error,connect-failure
spec:
rules:
- host: example.com
http:
paths:
- backend:
serviceName: example
servicePort: 80Downstream TLS certificates can be dynamically fetched and updated from Kubernetes secrets configured under ingresses' spec.tls by setting syncSecrets true in Yggdrasil configuration (false by default).
In this mode, only a single certificate may be specified in Yggdrasil configuration. It will be used for hosts with misconfigured or invalid secret.
Note: ECDSA >256 keys are not supported by envoy and will be discarded. See envoyproxy/envoy#10855
Yggdrasil can be configured using a config file e.g:
{
"nodeName": "foo",
"ingressClasses": ["multi-cluster", "multi-cluster-staging"],
"syncSecrets": false,
"certificates": [
{
"hosts": ["*.api.com"],
"cert": "path/to/cert",
"key": "path/to/key"
}
],
"clusters": [
{
"token": "xxxxxxxxxxxxxxxx",
"apiServer": "https://cluster1.api.com",
"ca": "pathto/cluster1/ca"
},
{
"tokenPath": "/path/to/a/token",
"apiServer": "https://cluster2.api.com",
"ca": "pathto/cluster2/ca"
}
]
}The list of certificates will be loaded by Yggdrasil and served to the Envoy nodes by inlining the key pairs. These will then be used to group the ingress into different filter chains, split using hosts.
nodeName is the same node-name that you start your envoy nodes with.
The ingressClasses is a list of ingress classes that yggdrasil will watch for.
Each cluster represents a different Kubernetes cluster with the token being a service account token for that cluster. ca is the Path to the ca certificate for that cluster.
Yggdrasil has a number of Go, gRPC, Prometheus, and Yggdrasil-specific metrics built in which can be reached by cURLing the /metrics path at the health API address/port (default: 8081). See Flags for more information on configuring the health API address/port.
The Yggdrasil-specific metrics which are available from the API are:
| Name | Description | Type |
|---|---|---|
| yggdrasil_cluster_updates | Number of times the clusters have been updated | counter |
| yggdrasil_clusters | Total number of clusters generated | gauge |
| yggdrasil_ingresses | Total number of matching ingress objects | gauge |
| yggdrasil_listener_updates | Number of times the listener has been updated | counter |
| yggdrasil_virtual_hosts | Total number of virtual hosts generated | gauge |
--address string yggdrasil envoy control plane listen address (default "0.0.0.0:8080")
--ca string trustedCA
--cert string certfile
--config string config file
--config-dump Enable config dump endpoint at /configdump on the health-address HTTP server
--debug Log at debug level
--envoy-listener-ipv4-address string IPv4 address by the envoy proxy to accept incoming connections (default "0.0.0.0")
--envoy-port uint32 port by the envoy proxy to accept incoming connections (default 10000)
--health-address string yggdrasil health API listen address (default "0.0.0.0:8081")
-h, --help help for yggdrasil
--host-selection-retry-attempts int Number of host selection retry attempts. Set to value >=0 to enable (default -1)
--http-ext-authz-allow-partial-message When this field is true, Envoy will buffer the message until max_request_bytes is reached (default true)
--http-ext-authz-cluster string The name of the upstream gRPC cluster
--http-ext-authz-failure-mode-allow Changes filters behaviour on errors (default true)
--http-ext-authz-max-request-bytes uint32 Sets the maximum size of a message body that the filter will hold in memory (default 8192)
--http-ext-authz-pack-as-bytes When this field is true, Envoy will send the body as raw bytes.
--http-ext-authz-timeout duration The timeout for the gRPC request. This is the timeout for a specific request. (default 200ms)
--http-grpc-logger-cluster string The name of the upstream gRPC cluster
--http-grpc-logger-name string Name of the access log
--http-grpc-logger-request-headers strings access logs request headers
--http-grpc-logger-response-headers strings access logs response headers
--http-grpc-logger-timeout duration The timeout for the gRPC request (default 200ms)
--ingress-classes strings Ingress classes to watch
--key string keyfile
--kube-config stringArray Path to kube config
--max-ejection-percentage int32 maximal percentage of hosts ejected via outlier detection. Set to >=0 to activate outlier detection in envoy. (default -1)
--node-name string envoy node name
--retry-on string default comma-separated list of retry policies (default "5xx")
--tracing-provider name of HTTP Connection Manager tracing provider to include - currently only zipkin config is supported
--upstream-healthcheck-healthy uint32 number of successful healthchecks before the backend is considered healthy (default 3)
--upstream-healthcheck-interval duration duration of the upstream health check interval (default 10s)
--upstream-healthcheck-timeout duration timeout of the upstream healthchecks (default 5s)
--upstream-healthcheck-unhealthy uint32 number of failed healthchecks before the backend is considered unhealthy (default 3)
--upstream-port uint32 port used to connect to the upstream ingresses (default 443)
--use-remote-address populates the X-Forwarded-For header with the client address. Set to true when used as edge proxy