Supporting Canary Deployments for Fission Functions
This tutorial will walk you through setting up a canary config to deploy a new version of a function on your cluster with minimal risk in a way that it gradually serves user traffic starting from 0% going all the way to 100% eventually.
Setup & pre-requisites
Canary feature can be enabled or disabled by setting a feature flag in helm chart
canaryDeployment.enabled to true or false during fission installation.
This feature is dependent on Prometheus metrics to check the health of the new version of the function. Hence, Prometheus is listed as a dependency for fission chart. Either an existing prometheus deployment in the cluster can be used or Prometheus could be installed alon with fission. To install prometheus with fission, the flag prometheusDeploy can be set to True in the helm chart. In order to re-use existing Prometheus deployment, fission checks the value of Prometheus server service environment variable in its controller pod. If that cant be accessed, fission proceeds without enabling the canary feature.
Canary Config parameters
A Canary Config has the following parameters :
duration: Specifies how frequently user traffic needs to be incremented for the new version of function
failurethreshold: Specifies the threshold in percentage beyond which the new version of a function is declared unhealthy
newfunction: Specifies the name of the latest version of the function
oldfunction: Specifies the name of the current stable version of the function
trigger: Specifies the name of the http trigger object
weightincrement: Specifies the percentage increase of user traffic towards the new version of the function
failureType: Specifies the parameter for checking the health of the new version of a function. For now, the only supported type is
status-codewhich is the http status code. So if a function returns a status code other than 200, its considered to be unhealthy.
For example, let’s say the current stable version of a function is fna-v1 and the latest version of a function is fna-v2. Let’s suppose we want to increment the traffic towards the new version in steps of 30% every 1m with a failure threshold of 10%. For such a scenario, the sample canary config is given below. What happens is that every 1m, the percentage of failed requests to fna-v2 gets calculated from prometheus metrics. If it is under the configured failure threshold of 10%, then the percentage traffic to fn-v2 gets incremented by 30% and this cycle repeats until either the failure threshold has reached at which point, the deployment is rolled back or fn-v2 is receiving 100% of the user traffic.
apiVersion: fission.io/v1 kind: CanaryConfig metadata: name: canary-1 namespace: default spec: duration: 1m failureType: status-code failurethreshold: 10 newfunction: fn-a-v2 oldfunction: fn-a-v1 trigger: route-fn-a weightincrement: 30
What happens is that every 1m, the percentage of failed requests to fn-a-v2 gets calculated from prometheus metrics. If it is under the configured failure threshold of 10%, then the percentage traffic to fn-a-v2 gets incremented by 30% and this cycle repeats until - either the failure threshold has reached at which point the deployment is rolled back, or, fn-v2 is receiving 100% of the user traffic.
Steps to setup a canary config
- Create an environment :
$ fission env create --name nodejs --image fission/node-env
- Create fission functions :
$ fission fn create --name fna-v1 --code hello.js --env nodejs $ fission fn create --name fna-v2 --code hello2.js --env nodejs
- Create an http trigger to these functions :
$ fission route create --name route-fn-a --function fna-v1 --weight 100 --function fna-v2 --weight 0
- Create a canary config :
$ fission canary-config create --name canary-1 --newfunction fna-v2 --oldfunction fna-v1 --httptrigger route-fn-a --increment-step 30 --increment-interval 1m --failure-threshold 10
Steps to verify the status of a canary deployment
$ fission canary-config get --name canary-1
This prints the status of the canary deployment of the new version of the function. 1. The status is “Pending” if the canary deployment is in progress. 2. The status is “Succeeded” if the new version of the function is receiving 100% of the user traffic. 3. The status is “Failed” if the failure threshold reached for the new version of the function and as a result 100% of the traffic gets routed to the old version of the function(rollback). 4. The status is “Aborted” if there were some failures during the canary deployment.
scrape_interval for Prometheus server is 1m by default. If the “duration” parameter needs to be less than 1m, the
scrape_interval parameter needs to configured to a much lower value.
This can be done by updating the config map for prometheus server. Just updating the config map is enough, prometheus server need not be restarted.