How to use Pkl in Docker with Golang?

[tikhonp]

Hello! I'm trying to dockerize my golang web project, here is source code, and after success build container, there is an error:

Attaching to server-1
server-1  | panic: –– Pkl Error ––
server-1  |     I/O error loading module `package://pkg.pkl-lang.org/pkl-go/[email protected]#/go.pkl`.
server-1  |     AccessDeniedException: /nonexistent
server-1  |
server-1  |     4 | import "package://pkg.pkl-lang.org/pkl-go/[email protected]#/go.pkl"
server-1  |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
server-1  |     at config#go (file:///pkl/config.pkl)
server-1  |
server-1  |     1 | @go.Package { name = "github.com/TikhonP/medsenger-freestylelibre-bot/config" }
server-1  |          ^^^^^^^^^^
server-1  |     at config (file:///pkl/config.pkl)
server-1  |
server-1  |
server-1  | goroutine 1 [running]:
server-1  | main.main()
server-1  |     /src/cmd/server/main.go:15 +0x110

My Dockerfile looks like this:

# syntax=docker/dockerfile:1

ARG GO_VERSION=1.23.0
ARG ALPINE_VERSION=3.20.2

FROM --platform=$BUILDPLATFORM golang:${GO_VERSION} AS build

WORKDIR /src

RUN --mount=type=cache,target=/go/pkg/mod/ \
    --mount=type=bind,source=go.sum,target=go.sum \
    --mount=type=bind,source=go.mod,target=go.mod \
    go mod download -x

ARG TARGETARCH

RUN --mount=type=cache,target=/go/pkg/mod/ \
    --mount=type=bind,target=. \
    CGO_ENABLED=0 GOARCH=$TARGETARCH go build -o /bin/server ./cmd/server


FROM alpine:${ALPINE_VERSION} AS final

RUN --mount=type=cache,target=/var/cache/apk \
    apk --update add \
        ca-certificates \
        tzdata \
        && \
        update-ca-certificates

ADD 'https://github.com/apple/pkl/releases/download/0.26.3/pkl-alpine-linux-amd64' /bin/pkl
RUN chmod +x /bin/pkl

ARG UID=10001
RUN adduser \
    --disabled-password \
    --gecos "" \
    --home "/nonexistent" \
    --shell "/sbin/nologin" \
    --no-create-home \
    --uid "${UID}" \
    tikhon
USER tikhon

COPY --from=build /bin/server /bin/
COPY pkl pkl

EXPOSE 9990

ENTRYPOINT [ "/bin/server" ]

pkl executable works in the container but reading config fails. Here my pkl file:

@go.Package { name = "github.com/TikhonP/medsenger-freestylelibre-bot/config" }
module config

import "package://pkg.pkl-lang.org/pkl-go/[email protected]#/go.pkl"

class Server {
  host: String
  port: UInt16
  medsengerAgentKey: String
  debug: Boolean
}

class Database {
  user: String
  password: String
  dbname: String
  host: String
}

server: Server
db: Database
fetchSleepDuration: Duration
sentryDSN: String

How to properly run pkl in a docker container?

[HT154]

The issue is that the user your application is running as has a home directory that doesn't exist. By default, Pkl will cache package access inside the home directory. You have two options here:

• Create/specify a real home directory for your app user
• Explicitly configure a cache directory your app user can write to https://github.com/apple/pkl-go/blob/3eebdd31069679a27c487aa82a9e7de33ecf114d/pkl/evaluator_options.go#L81

[StefMa]

You can also disable caching 🙃

[tikhonp]

Thank you! I tried configuring a cache directory and disabling cache, both works.
If it possible, it would be great to add more descriptive error message in this situation