Bump to go 1.20 (#836)

Switch the base images used for the Docker build to specify the golang
version, so we know what we're building for and can trigger rebuilds
when needed.

Dockerfile

@@ -1,5 +1,5 @@
 # download kubectl
-FROM golang:alpine3.16 as kubectl
+FROM golang:1.20.3-alpine as kubectl
 RUN apk add --no-cache curl
 RUN export VERSION=$(curl -s https://storage.googleapis.com/kubernetes-release/release/stable.txt) &&\
     export OS=$(go env GOOS) && \
@@ -8,7 +8,7 @@ RUN export VERSION=$(curl -s https://storage.googleapis.com/kubernetes-release/r
     chmod +x /usr/local/bin/kubectl
 
 # build jsonnet-bundler
-FROM golang:alpine3.16 as jb
+FROM golang:1.20.3-alpine as jb
 WORKDIR /tmp
 RUN apk add --no-cache git make bash &&\
     git clone https://github.com/jsonnet-bundler/jsonnet-bundler &&\
@@ -17,7 +17,7 @@ RUN apk add --no-cache git make bash &&\
     make static &&\
     mv _output/jb /usr/local/bin/jb
 
-FROM golang:alpine3.16 as helm
+FROM golang:1.20.3-alpine as helm
 WORKDIR /tmp/helm
 RUN apk add --no-cache jq curl
 RUN export TAG=$(curl --silent "https://api.github.com/repos/helm/helm/releases/latest" | jq -r .tag_name) &&\
@@ -26,7 +26,7 @@ RUN export TAG=$(curl --silent "https://api.github.com/repos/helm/helm/releases/
     curl -SL "https://get.helm.sh/helm-${TAG}-${OS}-${ARCH}.tar.gz" > helm.tgz && \
     tar -xvf helm.tgz --strip-components=1
 
-FROM golang:alpine3.16 as kustomize
+FROM golang:1.20.3-alpine as kustomize
 WORKDIR /tmp/kustomize
 RUN apk add --no-cache jq curl
 # Get the latest version of kustomize
@@ -40,7 +40,7 @@ RUN export TAG=$(curl --silent "https://api.github.com/repos/kubernetes-sigs/kus
     tar -xvf kustomize.tgz
 
 # assemble final container
-FROM alpine:3.16
+FROM alpine:3.17
 RUN apk add --no-cache coreutils diffutils less git openssh-client
 COPY tk /usr/local/bin/tk
 COPY --from=kubectl /usr/local/bin/kubectl /usr/local/bin/kubectl

go.mod

@@ -1,6 +1,6 @@
 module github.com/grafana/tanka
 
-go 1.19
+go 1.20
 
 require (
 	github.com/Masterminds/semver v1.5.0