diff --git a/R/cache.R b/R/cache.R
index 9e70a6d..1a817f8 100644
--- a/R/cache.R
+++ b/R/cache.R
@@ -143,11 +143,7 @@
     if (!dir.exists(cache_dir)) {
         dir.create(cache_dir, recursive = TRUE)
     }
-    sha <- .gh(paste0("/repos/debuerreotype/docker-debian-eol-artifacts/branches/dist-",
-                      debian_version))$commit$sha
-
-    debian_image_url <- .gh(paste0("/repos/debuerreotype/docker-debian-eol-artifacts/contents/",
-                                   debian_version, "/amd64/rootfs.tar.xz"), ref = sha)$download_url
+    debian_image_url <- debian_urls[debian_version]
     rootfs_path <- file.path(cache_dir, "rootfs.tar.xz")
     download.file(debian_image_url, destfile = rootfs_path, quiet = !verbose)
     if (!file.exists(rootfs_path)) {
diff --git a/R/dockerfile.R b/R/dockerfile.R
new file mode 100644
index 0000000..68e1e86
--- /dev/null
+++ b/R/dockerfile.R
@@ -0,0 +1,59 @@
+## .insert_cache_dir <- function(dockerfile_content) {
+##     rang_line <- which(dockerfile_content == "RUN Rscript rang.R")
+##     c(dockerfile_content[1:(rang_line - 1)],
+##       "COPY cache ./cache",
+##       dockerfile_content[rang_line:length(dockerfile_content)])
+## }
+
+.insert_materials_dir <- function(dockerfile_content) {
+    dockerfile_content$COPY <- append(dockerfile_content$COPY, "COPY materials/ ./materials/")
+    dockerfile_content
+}
+
+.generate_debian_eol_dockerfile_content <- function(r_version, lib, sysreqs_cmd, cache, debian_version = "lenny") {
+    dockerfile_content <- list(
+        FROM = c(paste0("FROM debian/eol:", debian_version)),
+        chores = c("ENV TZ UTC",
+                   "RUN ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone && apt-get update -qq && apt-get install wget locales build-essential r-base-dev  -y"),
+        COPY = c("COPY rang.R ./rang.R", "COPY compile_r.sh ./compile_r.sh"),
+        RUN = c(paste("RUN", sysreqs_cmd)),
+        CMD = c("CMD [\"R\"]"))
+    if (!is.na(lib)) {
+        dockerfile_content$RUN <- append(dockerfile_content$RUN, paste0("RUN mkdir ", lib, " && bash compile_r.sh ", r_version))
+    } else {
+        dockerfile_content$RUN <- append(dockerfile_content$RUN, paste0("RUN bash compile_r.sh ", r_version))
+    }
+    if (isTRUE(cache)) {
+        dockerfile_content$COPY <- append(dockerfile_content$COPY,
+                                          c("COPY cache/rpkgs ./cache/rpkgs", "COPY cache/rsrc ./cache/rsrc"))
+        dockerfile_content$FROM <- c("FROM scratch", "ADD cache/debian/rootfs.tar.xz /")
+    }
+    return(dockerfile_content)
+}
+
+.generate_rocker_dockerfile_content <- function(r_version, lib, sysreqs_cmd, cache, image) {
+    dockerfile_content <- list(
+        FROM = c(paste0("FROM rocker/", image, ":", r_version)),
+        chores = NULL,
+        COPY = c("COPY rang.R ./rang.R"),
+        RUN = c(paste("RUN", sysreqs_cmd)),
+        "CMD [\"R\"]")
+    if (!is.na(lib)) {
+        dockerfile_content$RUN <- append(dockerfile_content$RUN, paste0("RUN mkdir ", lib, " && Rscript rang.R"))
+    } else {
+        dockerfile_content$RUN <- append(dockerfile_content$RUN, "Rscript rang.R")
+    }
+    if (isTRUE(cache)) {
+        dockerfile_content$COPY <- append(dockerfile_content$COPY, "COPY cache ./cache")
+    }
+    if (image == "rstudio") {
+        dockerfile_content$RUN <- c("EXPOSE 8787", "CMD [\"/init\"]")
+    }
+    return(dockerfile_content)
+}
+
+.write_dockerfile <- function(dockerfile_content, path) {
+    content <- c(dockerfile_content$FROM, dockerfile_content$chores,
+                 dockerfile_content$COPY, dockerfile_content$RUN)
+    writeLines(content, path)
+}
diff --git a/R/installation.R b/R/installation.R
index 7044443..6b98f53 100644
--- a/R/installation.R
+++ b/R/installation.R
@@ -114,59 +114,6 @@
     utils::compareVersion(rang$r_version, r_version) == -1
 }
 
-.insert_cache_dir <- function(dockerfile_content) {
-    rang_line <- which(dockerfile_content == "RUN Rscript rang.R")
-    c(dockerfile_content[1:(rang_line - 1)],
-      "COPY cache ./cache",
-      dockerfile_content[rang_line:length(dockerfile_content)])
-}
-
-.insert_materials_dir <- function(dockerfile_content) {
-    rang_line <- which(dockerfile_content == "COPY rang.R ./rang.R")
-    c(dockerfile_content[1:rang_line],
-      "COPY materials/ ./materials/",
-      dockerfile_content[(rang_line + 1):length(dockerfile_content)])
-}
-
-.generate_debian_eol_dockerfile_content<- function(r_version, lib, sysreqs_cmd, cache, debian_version = "lenny") {
-    dockerfile_content <- c(
-        paste0("FROM debian/eol:", debian_version),
-        "ENV TZ UTC",
-        "RUN ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone && apt-get update -qq && apt-get install wget locales build-essential r-base-dev  -y",
-        "COPY rang.R ./rang.R",
-        "COPY compile_r.sh ./compile_r.sh",
-        paste("RUN", sysreqs_cmd),
-        paste("RUN bash compile_r.sh", r_version),
-        "CMD [\"R\"]")
-    if (!is.na(lib)) {
-        dockerfile_content[7] <- paste0("RUN mkdir ", lib, " && bash compile_r.sh ", r_version)
-    }
-    if (isTRUE(cache)) {
-        dockerfile_content <- c(dockerfile_content[1:5], "COPY cache/rpkgs ./cache/rpkgs", dockerfile_content[6:8])
-        dockerfile_content <- append(dockerfile_content, "COPY cache/rsrc ./cache/rsrc", after = 6)
-        dockerfile_content[1] <- "ADD cache/debian/rootfs.tar.xz /"
-        dockerfile_content <- c("FROM scratch", dockerfile_content)
-    }
-    return(dockerfile_content)
-}
-
-.generate_rocker_dockerfile_content <- function(r_version, lib, sysreqs_cmd, cache, image) {
-    dockerfile_content <- c("", "", "COPY rang.R ./rang.R", "RUN Rscript rang.R", "CMD [\"R\"]")
-    if (!is.na(lib)) {
-        dockerfile_content[4] <- paste0("RUN mkdir ", lib, " && Rscript rang.R")
-    }
-    dockerfile_content[1] <- paste0("FROM rocker/", image, ":", r_version)
-    dockerfile_content[2] <- paste("RUN", sysreqs_cmd)
-    if (image == "rstudio") {
-        dockerfile_content[5] <- "EXPOSE 8787"
-        dockerfile_content[6] <- "CMD [\"/init\"]"
-    }
-    if (isTRUE(cache)) {
-        dockerfile_content <- .insert_cache_dir(dockerfile_content)
-    }
-    return(dockerfile_content)
-}
-
 .generate_docker_readme <- function(output_dir,image) {
     file.create(file.path(output_dir,"README"))
     con <- file(file.path(output_dir,"README"), open="w")
@@ -428,7 +375,7 @@ dockerize <- function(rang, output_dir, materials_dir = NULL, image = c("r-ver",
                   recursive = TRUE)
         dockerfile_content <- .insert_materials_dir(dockerfile_content)
     }
-    writeLines(dockerfile_content, file.path(output_dir, "Dockerfile"))
+    .write_dockerfile(dockerfile_content, file.path(output_dir, "Dockerfile"))
     .generate_docker_readme(output_dir = output_dir,image = image)
     invisible(output_dir)
 }
diff --git a/R/memo_misc.R b/R/memo_misc.R
index c8b3262..6daa56e 100644
--- a/R/memo_misc.R
+++ b/R/memo_misc.R
@@ -56,7 +56,7 @@ NULL
 
 ## internal data generation
 ## ---
-### Supported OS Versions
+## ### Supported OS Versions
 ## supported_os <- c("trusty" = "ubuntu-14.04", "xenial" = "ubuntu-16.04", "bionic" = "ubuntu-18.04", "focal" = "ubuntu-20.04", "centos-6", "centos-7", "centos-8", "redhat-6", "redhat-7", "redhat-8")
 ## ### R version history
 ## cached_rver <- .rver()
@@ -64,7 +64,15 @@ NULL
 ## ### Bioconductor version history
 ## cached_biocver <- .biocver()
 ## attr(cached_biocver, "newest_date") <- max(cached_biocver$date)
-## usethis::use_data(supported_os, cached_rver, cached_biocver, internal = TRUE, overwrite = TRUE)
+## debian_version <- c("lenny", "squeeze", "wheezy", "jessie", "stretch")
+## .get_debian_urls <- function(debian_version, output_dir, verbose) {
+##     sha <- .gh(paste0("/repos/debuerreotype/docker-debian-eol-artifacts/branches/dist-",
+##                       debian_version))$commit$sha
+##     .gh(paste0("/repos/debuerreotype/docker-debian-eol-artifacts/contents/",
+##                debian_version, "/amd64/rootfs.tar.xz"), ref = sha)$download_url
+## }
+## debian_urls <- sapply(debian_version, .get_debian_urls)
+## usethis::use_data(supported_os, cached_rver, cached_biocver, debian_urls, internal = TRUE, overwrite = TRUE)
 
 ## test data upgrade
 ## ---
diff --git a/R/sysdata.rda b/R/sysdata.rda
index 40fab33..922b9c4 100644
Binary files a/R/sysdata.rda and b/R/sysdata.rda differ