Persist ENV in multi stage docker build
Is there a way to persist this ENV setting [across build stages]
No, there isn't.
An option would be including a pair of ARG:
ARG HTTP_PROXY=http://myproxy.comENV $HTTP_PROXYARG HTTPS_PROXY=https://myproxy.comENV $HTTPS_PROXYin every stage. Not very elegant, but it would let you pass --build-arg HTTP_PROXY=http://whatever.com etc on the command line, just once, and it would be set for all stages.
Another possibility, you could copy in a file from your host with these values defined:
# proxy.envHTTP_PROXY=http://myproxy.comHTTPS_PROXY=https://myproxy.comAnd just source it as needed in each stage:
FROM sentry:9.0-onbuildRUN source proxy.env && apt-get -qq update && DEBIAN_FRONTEND=noninteractive apt-get install -y -q libxslt1-dev libxml2-dev libpq-dev libldap2-dev libsasl2-dev libssl-devAlso kinda ugly, but at least you could keep the values consistent by defining them once somewhere, the file would be in VCS, and you wouldn't have to fool with passing --build-arg every build.