[Loki]: Cleanup dockerfile (#1949)

* Reduce the amount of layers and data in the Dockerfile

* Change the loki user and data directory to match the default helm configuration

* Add an nsswitch.conf to stop localhost DNS requests

* Copy changes to Dockerfile.cross except setep

setep is probably not needed anymore due to 3100 being the default
port. Also, I'm not sure the amd64 binary works on other arch
binaries.

* Install ca-certificates earlier and split creating user and creating dir steps

* Install libcap earlier and don't bother deleting it as it doesn't make the image smaller

* Revert config changes

* Revert the dockerfile changes needed for the config revert

cmd/loki/Dockerfile

@@ -7,21 +7,22 @@ WORKDIR /src/loki
 RUN make clean && (if [ "${TOUCH_PROTOS}" ]; then make touch-protos; fi) && make BUILD_IN_CONTAINER=false loki
 
 FROM alpine:3.9
-RUN apk add --update --no-cache ca-certificates libcap \
-    && rm -rf /var/cache/apk/*
+
+RUN apk add --no-cache ca-certificates libcap
 
 COPY --from=build /src/loki/cmd/loki/loki /usr/bin/loki
 COPY cmd/loki/loki-docker-config.yaml /etc/loki/local-config.yaml
 
 RUN setcap cap_net_bind_service=+ep /usr/bin/loki
 
-RUN apk del --no-cache libcap && rm -rf /var/cache/apk/*
-
-RUN addgroup -g 1000 -S loki && \
-    adduser -u 1000 -S loki -G loki
+RUN addgroup -g 10001 -S loki && \
+    adduser -u 10001 -S loki -G loki
 RUN mkdir -p /loki && \
     chown -R loki:loki /etc/loki /loki
 
+# See https://github.com/grafana/loki/issues/1928
+RUN [ ! -e /etc/nsswitch.conf ] && echo 'hosts: files dns' > /etc/nsswitch.conf
+
 USER loki
 EXPOSE 3100
 ENTRYPOINT [ "/usr/bin/loki" ]

cmd/loki/Dockerfile.cross

@@ -13,9 +13,21 @@ WORKDIR /src/loki
 RUN make clean && GOARCH=$(cat /goarch) GOARM=$(cat /goarm) make BUILD_IN_CONTAINER=false loki
 
 FROM alpine:3.9
-RUN apk add --update --no-cache ca-certificates
+
+RUN apk add --no-cache ca-certificates
+
 COPY --from=build /src/loki/cmd/loki/loki /usr/bin/loki
 COPY cmd/loki/loki-local-config.yaml /etc/loki/local-config.yaml
-EXPOSE 80
+
+RUN addgroup -g 10001 -S loki && \
+    adduser -u 10001 -S loki -G loki
+RUN mkdir -p /loki && \
+    chown -R loki:loki /etc/loki /loki
+
+# See https://github.com/grafana/loki/issues/1928
+RUN [ ! -e /etc/nsswitch.conf ] && echo 'hosts: files dns' > /etc/nsswitch.conf
+
+USER loki
+EXPOSE 3100
 ENTRYPOINT [ "/usr/bin/loki" ]
 CMD ["-config.file=/etc/loki/local-config.yaml"]