don't mount /var/log as readonly (#314)

* don't mount /var/log as readonly

* update phrasing in changelog to explain what the issue was

CHANGELOG.md

@@ -13,6 +13,10 @@ this platform. FreeBSD builds will return in a future release.
 - [BUGFIX] Integrations will now function if the HTTP listen address was set to
   a value other than the default. ([#206](https://github.com/grafana/agent/issues/206)) (@mattdurham) 
 
+- [BUGFIX] The default Loki installation will now be able to write its positions
+  file. This was prevented by accidentally writing to a readonly volume mount.
+  (@rfratto)
+
 # v0.9.1 (2021-01-04)
 
 NOTE: FreeBSD builds will not be included for this release. There is a bug in an

production/kubernetes/agent-loki.yaml

@@ -338,7 +338,6 @@ spec:
           name: grafana-agent-logs
         - mountPath: /var/log
           name: varlog
-          readOnly: true
         - mountPath: /var/lib/docker/containers
           name: varlibdockercontainers
           readOnly: true

production/tanka/grafana-agent/v1/lib/loki.libsonnet

@@ -67,8 +67,9 @@ local container = k.core.v1.container;
       container.mixin.securityContext.withRunAsUser(0),
 
     agent+:
-      // For reading docker containers
-      k.util.hostVolumeMount('varlog', '/var/log', '/var/log', readOnly=true) +
+      // For reading docker containers. /var/log is used for the positions file
+      // and shouldn't be set to readonly.
+      k.util.hostVolumeMount('varlog', '/var/log', '/var/log') +
       k.util.hostVolumeMount('varlibdockercontainers', '/var/lib/docker/containers', '/var/lib/docker/containers', readOnly=true) +
 
       // For reading journald